there are sock errors on the network connection between the nodes.

===
block drbd0: [drbd0_worker/21962] sock_sendmsg time expired, ko = 4294967142
block drbd0: sock_recvmsg returned -110
block drbd0: sock_sendmsg returned -32
block drbd0: peer( Secondary -> Unknown ) conn( WFBitMapS -> BrokenPipe ) pdsk( UpToDate -> DUnknown )
block drbd0: short read expecting header on sock: r=-110
block drbd0: short sent ReportBitMap size=4096 sent=1504
===

reset the DRDB configuration to default and see if it works

default values:
max-buffers=2048
max-epoch-size=2048
unplug-watermark=128
sndbuf-size=0
al-extents=127
no-disk-barrier=off
no-disk-flushes=off