It means, map from server is different than in your own game.
One of those maps have either re-compiled or have made some tinkering.
Maps have own
CRC check code when Hammer editor have compiled map.
- If someone compile another map with same name, there is different CRC code then.
If you enable logging, you see this log message when change map.
Code:
L 01/26/2024 - 00:05:58: Started map "c1m1_hotel" (CRC "-1242577269")
Steamcmd Update with -validate , like you did already, fix it. Expect if this problem relate custom maps.
Good that you solved your problem already.
*ps
People sometimes had make mistake, set same named map, with different version, to fast download and server. So clients always download wrong map than what server run.