From a technical perspective it is MySQL where we are having the issue. Previously the site was running on a single server with no HA. Now it's running off multiple servers and the forum is connecting through MaxScale to MySQL , it is MaxScale that provides HA to MySQL stack, which was having an issue connecting to MySQL on one server. So as the traffic is splitting over the servers, when you hit the one having the issue you got the messages. We have more logging enabled trying to track down the root cause so will see how we go tonight and hopefully crack it.
Some of the errors early on pointed to the plugins to the forum so threw us off a bit in the wrong direction for a while.
The joys of new setups and fine tuning!
We will get there and thanks for the patience while we get it all dialled in.