[ClusterLabs] weird corosync - [TOTEM ] FAILED TO RECEIVE

[lejeczek]

hi guys,
I have a 3-node cluser(centos 7.5), 2 nodes seems fine but 
third(or probably something else in between) is not right.
I see this:

  $ pcs status --all
Cluster name: CC
Stack: corosync
Current DC: whale.private (version 
1.1.18-11.el7_5.3-2b07d5c5a9) - partition with quorum
Last updated: Fri Oct 12 15:40:39 2018
Last change: Fri Oct 12 15:14:57 2018 by root via 
crm_resource on whale.private

3 nodes configured
8 resources configured (1 DISABLED)

Online: [ rental.private whale.private ]
OFFLINE: [ rider.private ]

and that third node logs:

[TOTEM ] FAILED TO RECEIVE
  [TOTEM ] A new membership (10.5.6.100:2504344) was formed. 
Members left: 2 4
  [TOTEM ] Failed to receive the leave message. failed: 2 4
  [QUORUM] Members[1]: 1
  [MAIN  ] Completed service synchronization, ready to 
provide service.
  [TOTEM ] A new membership (10.5.6.49:2504348) was formed. 
Members joined: 2 4
  [TOTEM ] FAILED TO RECEIVE

and it just keeps going like that.
Sometimes reboot(or stop of services + wait + start) of that 
third node would help.
But, I get this situation almost every time a node gets 
(orderly) shut down or reboot.
Network-wise, connectivity, seem okey. Where to start?

many thanks, L