Is the system date/time correct? If not, you can try using zentyal-ntp to fix it. Just an idea, I'm not sure if that's the cause of the problem...
Yes, I actually have zentyal ntp enabled on this server and the rest of my servers. All the times are in sync. I have been monitoring the server throughout the day and have not noticed any additional "TLS keys are out of sync" errors but I have gotten a few timeout errors to 92.243.6.103; but I've seen these in the past. Updating the client side to use TCP for Zentyal Cloud has seemed to have fixed the issue (for now).
What I don't understand is, why did this only impact this server? My other three servers have not had any of these issue. And yes, I did verify that the other three servers are only using UDP as the protocol. Interesting?