Warning for "missing node in relation" not comprehensible

[double-a]

I just wanted to fix some warnings for Germany/Munich S-Bahn and I do not get the underlying issue:
The dataset is missing the railway tracks node n91213610 (relation 12193416, "RB 66: München => Tutzing => Kochel")
AFAIK the relation collects all lines of the track and individual nodes for stops/platforms.
But the referenced node has no such attribute, thus why is this node missing?
Sorry for bothering...

[alexey-zakharenkov]

The dataset is the data source for the validator, it may be prepared in different ways such as planet.osm.pbf filtering, overpass query or manually edited xml. Missing node stands for a way/relation is referencing a node that is absent in the dataset. The most common case requires extending the bounding box for the network in the list https://docs.google.com/spreadsheets/d/1SEW1-NiNOnA2qDwievcxYV1FOaQl1mb1fdeyqAxHu3k/edit#gid=112805400 (commenting allowed). I'll examine all such errors shortly.