Forced closure of a channel is stuck and its blocks_til_maturity value is negative.

[25shmeckles]

Background

One of my peers forced the closure of a channel with me. After a few days, the closure is still pending, and the blocks_til_maturity variable went from positive to negative and continues to add -1 for each block. How is this even possible? How to fix it?

Your environment

• LND 0.17.3-beta
• Linux 5.15.0-89-generic (Linux Mint Tessa)
• bitcoind Bitcoin Core version v25.0.0
• Node Public Key: 022d509049e143b1c5fc5383210acb97a3e5a4b0e0d31dd4c920eee92a4aacd312

Steps to reproduce

Expected behaviour

I expect the channel to be closed once the time_til_maturity reaches 0

Actual behaviour

The channel is stuck even if the blocks_til_maturity value goes 0. The count actually didn't stop and now the value is negative!

$ lncli pendingchannels
...
"pending_force_closing_channels":  [
        {
            "channel":  {
                "remote_node_pub":  "02907887f9bfcc9e83512bfdf40ddfdabcb8569786f11ac3e9c52c42d77da3eb6b",
                "channel_point":  "163369b95ee782dc403c11ea33b596c762b98e19bb84826809e536955d38a691:0",
                "capacity":  "116595",
                "local_balance":  "7874",
                "remote_balance":  "105250",
                "local_chan_reserve_sat":  "0",
                "remote_chan_reserve_sat":  "0",
                "initiator":  "INITIATOR_REMOTE",
                "commitment_type":  "ANCHORS",
                "num_forwarding_packages":  "0",
                "chan_status_flags":  "",
                "private":  false,
                "memo":  ""
            },
            "closing_txid":  "6ada89df0b10973bc82e30148301e13c8ead6683b1decff684c713d2bd13e2d9",
            "limbo_balance":  "8204",
            "maturity_height":  820319,
            "blocks_til_maturity":  -280,
            "recovered_balance":  "0",
            "pending_htlcs":  [],
            "anchor":  "LIMBO"
        }
    ],
...

Other channels are also stuck in "waiting_close_channels" status for days, and when I try to --force close them, I get:
[lncli] RPC error: code = Unknown desc = channel is already in the process of being force closed even though they are not listed under "pending_force_closing_channels".
Perhaps the two problems are related.

"waiting_close_channels": [
        {
            "channel": {
                "remote_node_pub": "027aacfeeaa24fa5580324ae3803577f47a8dd8f43344dfc306991fae6e399bdab",
                "channel_point": "cf7b9aa50a48a692d4a9ec6b705aa83b9f4db26f5a8d23790c1abb04770c567d:0",
                "capacity": "100000",
                "local_balance": "93369",
                "remote_balance": "4082",
                "local_chan_reserve_sat": "1000",
                "remote_chan_reserve_sat": "1000",
                "initiator": "INITIATOR_REMOTE",
                "commitment_type": "STATIC_REMOTE_KEY",
                "num_forwarding_packages": "0",
                "chan_status_flags": "ChanStatusBorked|ChanStatusCommitBroadcasted|ChanStatusLocalCloseInitiator",
                "private": false,
                "memo": ""
            },
            "limbo_balance": "93369",
            "commitments": {
                "local_txid": "39b16318b275bb633a73b2d43330ed121d25d26d8e5a0a5a26f838bd463461cc",
                "remote_txid": "0053441ebb6fcee5fb0837bdf8583c0bbc0b29b1f3f88c3d35297a7fda54353d",
                "remote_pending_txid": "",
                "local_commit_fee_sat": "2548",
                "remote_commit_fee_sat": "2548",
                "remote_pending_commit_fee_sat": "0"
            },
            "closing_txid": "39b16318b275bb633a73b2d43330ed121d25d26d8e5a0a5a26f838bd463461cc"
        },
        {
            "channel": {
                "remote_node_pub": "030a0274ea8e172060973a34d0d81e55a67e8ce22222b0c50b626ac5dd5d8dbf5e",
                "channel_point": "c77e194a52e212e4c15c226d636ef8874890b5297a3a95f7b56503491ac76cf2:1",
                "capacity": "311365",
                "local_balance": "296813",
                "remote_balance": "11081",
                "local_chan_reserve_sat": "3113",
                "remote_chan_reserve_sat": "3113",
                "initiator": "INITIATOR_REMOTE",
                "commitment_type": "ANCHORS",
                "num_forwarding_packages": "4",
                "chan_status_flags": "ChanStatusBorked|ChanStatusCommitBroadcasted|ChanStatusLocalCloseInitiator",
                "private": false,
                "memo": ""
            },
            "limbo_balance": "296813",
            "commitments": {
                "local_txid": "c8e2c8ae801b4ade0549c579f894742ed0bd4d45e1066f6c92a0e1537c697316",
                "remote_txid": "9407e19041246ca518f87f29727d0df88005d95294d8d72707ec036ce7c4270e",
                "remote_pending_txid": "",
                "local_commit_fee_sat": "2810",
                "remote_commit_fee_sat": "2810",
                "remote_pending_commit_fee_sat": "0"
            },
            "closing_txid": "c8e2c8ae801b4ade0549c579f894742ed0bd4d45e1066f6c92a0e1537c697316"
        },
        {
            "channel": {
                "remote_node_pub": "033559715be17024975142eb36a7ae2866efb0842523c86adc86a413171857b08f",
                "channel_point": "11c9da8a7c05cd671f7957163592832463e4c6d893d1628ac6a96810ddd8cccb:0",
                "capacity": "1000000",
                "local_balance": "0",
                "remote_balance": "996530",
                "local_chan_reserve_sat": "10000",
                "remote_chan_reserve_sat": "10000",
                "initiator": "INITIATOR_REMOTE",
                "commitment_type": "ANCHORS",
                "num_forwarding_packages": "0",
                "chan_status_flags": "ChanStatusBorked|ChanStatusCommitBroadcasted|ChanStatusLocalCloseInitiator",
                "private": false,
                "memo": ""
            },
            "limbo_balance": "0",
            "commitments": {
                "local_txid": "f80dc164756fabb169332f0ec3508213ab0a1d75caf9c799a4a538067339520c",
                "remote_txid": "3bf9258d2f644216435b67a7725c7300fd141175721d3e48ae0d99ab3d548b62",
                "remote_pending_txid": "",
                "local_commit_fee_sat": "2810",
                "remote_commit_fee_sat": "2810",
                "remote_pending_commit_fee_sat": "0"
            },
            "closing_txid": "f80dc164756fabb169332f0ec3508213ab0a1d75caf9c799a4a538067339520c"
        },
        {
            "channel": {
                "remote_node_pub": "03b224e9ab3df5fae46b73a56c1a899fe507fcdf78338d9463c73e682ee3b90e04",
                "channel_point": "b9e1390313120c954efa8f727bf9c955e03b7557a7fdd2129c4576bea369b010:0",
                "capacity": "500000",
                "local_balance": "475759",
                "remote_balance": "20887",
                "local_chan_reserve_sat": "5000",
                "remote_chan_reserve_sat": "5000",
                "initiator": "INITIATOR_REMOTE",
                "commitment_type": "ANCHORS",
                "num_forwarding_packages": "0",
                "chan_status_flags": "ChanStatusBorked|ChanStatusCommitBroadcasted|ChanStatusLocalCloseInitiator",
                "private": false,
                "memo": ""
            },
            "limbo_balance": "475759",
            "commitments": {
                "local_txid": "ed520861063bbabcad67a45732a4602bb70dc0e0a4d5175484d35fe8bd3d77a6",
                "remote_txid": "8947d157982f4e53a74e21a55f2f60cf244ba3fb7bf056727d43b9fa320e7ed0",
                "remote_pending_txid": "",
                "local_commit_fee_sat": "2693",
                "remote_commit_fee_sat": "2693",
                "remote_pending_commit_fee_sat": "0"
            },
            "closing_txid": "ed520861063bbabcad67a45732a4602bb70dc0e0a4d5175484d35fe8bd3d77a6"
        }
    ]

[bitromortac]

The pending channel is almost resolved, you didn't sweep the anchor yet ("anchor": "LIMBO"), which probably doesn't make sense with this fee environment, but this is expected I think. There also are no time-critical HTLCs on your commitment transaction, so it is fine to wait until it can be resolved.

Your other channels are waiting for confirmation. Unfortunately all of those have low commitment transaction fees. For the non-anchor one you will need to wait for 14 sat/vbyte to confirm. For the anchor channels I'm not sure why they are not fee bumped, they don't seem to have any htlcs on them and have low ctx fees as well (10, 10, and 16 sat/vbyte). At least the force close transactions can be seen on mempool.space, so it means that they propagated at least to some extent.

[25shmeckles]

Thanks for the heads up. I'll wait. I was just puzzled by the negative value of the blocks_til_maturity; I never noticed that before. What do you mean by "sweep the anchor"?

[bitromortac]

A negative value means that we are past an HTLC deadline, but since there's no HTLC on the transaction, I think that's nothing to worry about and of informational character.

The anchor output is a small-value extra output (330 sat, see) that's used to increase the fee of a transaction by spending the output with a higher fee rate to control how fast it confirms (the keyword is CPFP). Your transaction is already confirmed, so sweeping or claiming the 330 sat output here costs more than you get, so it is delayed.

[saubyk]

Moving this issue to a discussion, as there is nothing to fix here

[bitromortac]

You could try lncli wallet bumpclosefee on an anchor channel to see if it spends the anchor and increases the closing fee.