Do you have a full log with such an error? (Ideally with knowing the time it happened in the log 
)
Typically that's caused by the client closing the connection, so in that case CSMM. Reconnecting afterwards should be fine though, but I'm not sure what Cata has implemented in that regard.
/EDIT 1: When it happens, can you still use the game's web dashboard to look at the log output?
/EDIT 2: Do you also use the game's web dashboard for the server? If so, is it only you or are there a bunch of people accessing it at the same time, possibly permanently with the console / log section open?
/EDIT 3: Re edit1: When it happens, can you still use the game's webdashboard in general (so *both* log output specifically as well as other functions like looking at settings or whatever or even just reloading the page)