I routinely receive this message every time that I play, generally within the first sixty to ninety minutes. I see many complaints about this on the forum, but no one seems to have mentioned the specifics that I experience.
Most suggest that this message is due to a server restart and I, too, have experienced this. More commonly, however, whenever I experience this, when I log back into the same server, it has not restarted (based on the game time), but it has started to rain.
I would conservatively estimate that whenever I loose connection to the server, along with this message, 90-95% of the time it will be raining when I log back in.