diff --git a/agent/Makefile b/agent/Makefile
index a2334a7e7d..a4cfc32532 100644
--- a/agent/Makefile
+++ b/agent/Makefile
@@ -25,7 +25,7 @@ VERSION_FLAGS = -X 'github.com/percona/pmm/version.ProjectName=pmm-agent' \
 				-X 'github.com/percona/pmm/version.Branch=$(PMM_RELEASE_BRANCH)'
 
 release:                        ## Build static pmm-agent release binary (Linux only)
-	env CGO_ENABLED=1 go build -v -ldflags "-extldflags '-static' $(VERSION_FLAGS)" -tags 'osusergo netgo static_build' -o $(PMM_RELEASE_PATH)/pmm-agent
+	env CGO_ENABLED=1 go build -race -v -ldflags "-extldflags '-static' $(VERSION_FLAGS)" -tags 'osusergo netgo static_build' -o $(PMM_RELEASE_PATH)/pmm-agent
 	go build -v -ldflags "-extldflags '-static' $(VERSION_FLAGS)" -tags 'osusergo netgo static_build' -o $(PMM_RELEASE_PATH)/pmm-agent-entrypoint ./cmd/pmm-agent-entrypoint
 	$(PMM_RELEASE_PATH)/pmm-agent --version
 	ldd $(PMM_RELEASE_PATH)/pmm-agent 2>&1 | grep -Fq 'not a dynamic executable'
diff --git a/agent/client/client.go b/agent/client/client.go
index f6ba5547a7..bf8888ef21 100644
--- a/agent/client/client.go
+++ b/agent/client/client.go
@@ -173,11 +173,11 @@ func (c *Client) Connect(ctx context.Context) error {
 	}()
 	c.supervisor.ClearChangesChannel()
 	c.SendActualStatuses()
-	c.cache.SetSender(dialResult.channel)
 
 	c.rw.Lock()
 	c.md = dialResult.md
 	c.channel = dialResult.channel
+	c.cache.SetSender(dialResult.channel)
 	c.rw.Unlock()
 
 	c.processChannelRequests(ctx)
diff --git a/agent/utils/buffer-ring/bigqueue/bigqueue.go b/agent/utils/buffer-ring/bigqueue/bigqueue.go
index 8bc35b8472..67ee768774 100644
--- a/agent/utils/buffer-ring/bigqueue/bigqueue.go
+++ b/agent/utils/buffer-ring/bigqueue/bigqueue.go
@@ -56,7 +56,7 @@ type Ring struct {
 	wg sync.WaitGroup
 
 	sendLock  sync.RWMutex
-	recvLock  sync.RWMutex
+	recvLock  sync.Mutex
 	totalSize int64 // represent the limit after which old data will be overwritten
 
 	sender atomic.Pointer[models.Sender]
@@ -123,20 +123,20 @@ func (r *Ring) Send(resp *models.AgentResponse) error {
 
 	r.recvLock.Lock()
 	defer r.recvLock.Unlock()
-	if r.isEmpty() && s != nil {
-		err = (*s).Send(resp)
-		if err != nil && errors.As(err, &agenterrors.ErrChanConn) {
-			if r.sender.CompareAndSwap(s, nil) {
-				asyncRelease(r.establishCh)
-				r.l.Debugf("sender released: %v", err)
-			}
-		} else {
-			return err
+	if !r.isEmpty() || s == nil {
+		r.push(msg)
+		return nil
+	}
+	err = (*s).Send(resp)
+	if errors.As(err, &agenterrors.ErrChanConn) {
+		if r.sender.CompareAndSwap(s, nil) {
+			asyncRelease(r.establishCh)
+			r.l.Debugf("sender released: %v", err)
+			r.push(msg)
 		}
+		return nil
 	}
-
-	r.push(msg)
-	return nil
+	return err
 }
 
 // SendAndWaitResponse stores AgentMessageRequestPayload on nil channel.
@@ -149,20 +149,23 @@ func (r *Ring) SendAndWaitResponse(payload agentpb.AgentRequestPayload) (agentpb
 
 	r.recvLock.Lock()
 	defer r.recvLock.Unlock()
-	if r.isEmpty() && s != nil {
-		resp, err = (*s).SendAndWaitResponse(payload)
-		if err != nil && errors.As(err, &agenterrors.ErrChanConn) {
-			if r.sender.CompareAndSwap(s, nil) {
-				asyncRelease(r.establishCh)
-				r.l.Debugf("sender released: %v", err)
-			}
-		} else {
-			return resp, err
+
+	if !r.isEmpty() || s == nil {
+		r.push(&agentpb.AgentMessage{Payload: payload.AgentMessageRequestPayload()})
+		return nil, nil
+	}
+
+	resp, err = (*s).SendAndWaitResponse(payload)
+	if err != nil && errors.As(err, &agenterrors.ErrChanConn) {
+		if r.sender.CompareAndSwap(s, nil) {
+			asyncRelease(r.establishCh)
+			r.l.Debugf("sender released: %v", err)
 		}
+		r.push(&agentpb.AgentMessage{Payload: payload.AgentMessageRequestPayload()})
+		return nil, nil
 	}
 
-	r.push(&agentpb.AgentMessage{Payload: payload.AgentMessageRequestPayload()})
-	return &agentpb.StateChangedResponse{}, nil
+	return resp, err
 }
 
 // SetSender check and set sender and notify sender loop.
@@ -179,6 +182,8 @@ func (r *Ring) Close() {
 	default:
 		close(r.done)
 		r.wg.Wait()
+		r.recvLock.Lock()
+		defer r.recvLock.Unlock()
 		if err := r.fq.Close(); err != nil {
 			r.l.Errorf("closing cache: %+v", err)
 		}
@@ -190,6 +195,7 @@ func (r *Ring) isEmpty() bool {
 	return r.fq.IsEmpty()
 }
 
+// push inserts message to cache.
 func (r *Ring) push(msg *agentpb.AgentMessage) {
 	b, err := proto.Marshal(msg)
 	if err != nil {
@@ -261,6 +267,7 @@ func (r *Ring) sendRunner() {
 	}()
 }
 
+// sendInLoop sends messages from cache to sender.
 func (r *Ring) sendInLoop() {
 	var s *models.Sender
 	for {
@@ -284,35 +291,47 @@ func (r *Ring) sendInLoop() {
 			return
 		default:
 		}
-		r.recvLock.Lock()
-		_, b, err := r.fq.Peek()
-		r.recvLock.Unlock()
-		if err != nil {
-			r.l.Errorf("reading entry from cache: %+v", err)
-		}
-		if b == nil {
-			break
-		}
-		var m agentpb.AgentMessage
-		if err := proto.Unmarshal(b, &m); err != nil {
-			r.l.Errorf("unmarshal entry from cache: %+v", err)
-		} else if err = r.send(*s, &m); err != nil {
-			if r.sender.CompareAndSwap(s, nil) {
-				asyncRelease(r.establishCh)
-				r.l.Debugf("sender released: %v", err)
-			}
-			break
-		}
-		r.recvLock.Lock()
-		r.fq.Skip(1) //nolint:errcheck
-		r.recvLock.Unlock()
-		count++
+		count += r.peekAndSend(s)
 	}
 	if count > 0 {
 		asyncNotify(r.gcCh)
 	}
 }
 
+func (r *Ring) peekAndSend(s *models.Sender) int {
+	defer func() {
+		if rc := recover(); rc != nil {
+			r.l.Errorf("panic in peekAndSend: %v", rc)
+		}
+	}()
+	r.recvLock.Lock()
+	r.l.Debugf("status: %v", r.fq.Status())
+	idx, b, err := r.fq.Peek()
+	r.recvLock.Unlock()
+	if err != nil {
+		r.l.Errorf("reading entry from cache: %+v", err)
+	}
+	if len(b) == 0 {
+		return 0
+	}
+	r.l.Debugf("resending %d: %s", idx, string(b))
+	var m agentpb.AgentMessage
+	err = proto.Unmarshal(b, &m)
+	if err != nil {
+		r.l.Errorf("unmarshal entry from cache: %+v", err)
+	} else if err = r.send(*s, &m); err != nil {
+		if r.sender.CompareAndSwap(s, nil) {
+			asyncRelease(r.establishCh)
+			r.l.Debugf("sender released: %v", err)
+		}
+		return 0
+	}
+	r.recvLock.Lock()
+	r.fq.Skip(1) //nolint:errcheck
+	r.recvLock.Unlock()
+	return 1
+}
+
 // initPaths creates all paths for queue to use. Original repo creates directories with perm error.
 func initPaths(dir string) error {
 	for _, path := range []string{
@@ -405,7 +424,7 @@ func (r *Ring) send(s models.Sender, m *agentpb.AgentMessage) error {
 	case *agentpb.AgentMessage_StateChanged:
 		_, err = s.SendAndWaitResponse(p.StateChanged)
 	default:
-		r.l.Errorf("unknown message: %T", m)
+		r.l.Warnf("unknown message in cache: %T", m)
 		return nil
 	}
 	if err != nil && errors.As(err, &agenterrors.ErrChanConn) {
diff --git a/update/ansible/playbook/tasks/roles/initialization/tasks/main.yml b/update/ansible/playbook/tasks/roles/initialization/tasks/main.yml
index 5113096993..81c57b7ff4 100644
--- a/update/ansible/playbook/tasks/roles/initialization/tasks/main.yml
+++ b/update/ansible/playbook/tasks/roles/initialization/tasks/main.yml
@@ -220,12 +220,10 @@
         method: GET
       retries: 120
       delay: 1
-
-    - name: Disable maintenance mode
-      file:
-        state: absent
-        path: /usr/share/pmm-server/maintenance/maintenance.html
   # We use current_version_file['failed'] because we don't want to run this on creating container
   when: docker_upgrade
 
-
+- name: Disable maintenance mode
+  file:
+    state: absent
+    path: /usr/share/pmm-server/maintenance/maintenance.html