Random client disconnects from server

I've seen a few posts about this but not any solutions. I'm experiencing random client disconnects in my application. The clients log in fine but then the server just loses them. They remain connected, but the server doesn't see them any longer and their names are dropped from the connected user list. The event logs aren't helpful, they just show that the client disconnected.

Any ideas on what could be causing this? I feel like it must be some sort of network error because it never happens during testing, but with certain users it's more common.