11.4.0 Peer device "disconnected" but syncing

Hello all

Last week I upgraded a pair of BIG-IP 6900 from 10.2.2 to 11.4.0, following the recommended procedure for active-standby configurations.

Once both nodes were upgraded, I noticed that in the screen "Device Group" each node saw the peer as "Disconnected" (red dot). However, the sync was working, and also did the failover, as I tried forcing the active node to standby and the other one became active immediately.

I tried resetting the trust but the situation was the same. I attach a screenshot of Device Group (I have shadowed the hostnames for privacy). This is from one of the nodes, the other one shows the equivalent.

I wonder if any of you have encountered a similar issue, and whether you know how I could solve it. I guess maybe it is a silly parameter I forgot to configure, but I can't manage to figure out which one, so any help would be appreciated.

If you need further information, please let me know.

Thanks in advance.