That behaviour happens when a certain server is switched during a game (usually for performanc reasons). During the game everything works, but afterwards the game logs you out.
Unfortunately, there is no in-game way to get the game number. If it was a rated 2-player game, "Dombot" (on the Dominion discord) can list your last rated games with the "!prior Ingix" command (replace Ingix with your in-game name). If you played several games vs. the same player (even unrated) in a row, it will list those games when you ask it "!match Ingix, Stef" (with in-game names of both players replacing Ingix and Stef).
In both cases, it will list you game numbers, the kingdom and the point result. If you find the game (check the kingdom), you can get more detailed results by asking it "!game 12345678" (put in the the game number at the end).