A few things can cause the problem you describe. The server could be occasionally crashing right at a map change (unlikely), the mapchange could be taking longer than usual to load, or the connection might have been broken between you and the server for some other reason.
If this starts happening to you a lot, I'd recommend raising cl_timeout on the client side, and sv_timeout on the server side if that doesn't fix it. That will give the maps longer to load before either side disconnects, if that is what is causing your problems.
In addition, if this starts happening frequently to everyone in the server, I will definitely need take a look at it on my end. Please keep me posted!