OpenVPN clients disconnecting
We've been using a PfSense firewall with OpenVPN for some remote CentOS clients for over a year now. It's been totally reliable with no issues - until last week. Suddenly, connected clients will randomly disconnect, and when they do, it's all at the same time. They'll then re-connect ok, but will drop again at a later time. There have been no config or infrastructure changes, and all other traffic traversing in/out of the site is working fine. This was a v2.4.4 server, which I've now replaced with a 2.5.1 version (config migrated across). It seemed better initially, but the same disconnections are still happening, but maybe slightly less frequently.
Nothing logged on the server (other than the disconnections), and nothing in the logs on the clients either. I've tried playing around with serve-side keepalive settings (never had to before), but it's still erratic. This is crazy, and so annoying. The connection from the clients is relative simple - <client> -> <external firewall (passthrough UDP1194/TCP443)> -> <PfSense instance>
I've checked everything I can think of, so any ideas at all?