Adding my 2 cents as well. We recently upgraded to 2306 and seeing the error as well, but only concerning internal Connection Servers, my UAG's are showing all green.

I sent my "LB Guy" the relevant VMware KB's, but he can't find anything wrong.

Looking at the debug logs, we see the following lines, but searches haven't turned up anything of value (except this thread).

Nothing immediately immediately before or following this entry provides any relevant information either.

<MessageFrameWorkDispatch> [MessageFrameWork] KeyVaultWorker::MessageHandler(): KeyVault service got operation=decipherWithDerivedKey, ok=1, msecs=16
<ajp-nio-127.0.0.1-8009-exec-1> [ConnectionServerHandler] Incrementing the warning count : Reason : unrecognized request detected