Are you using
workshop maps ?
My guess is 1) your server lost Steam connection temporary 2) one of workshop maps is not active anymore on Steam site.
You can try this:
[CSGO] End of Match - Stuck!
*edit
If you not use workshop maps, then you need give us more details. Like what kind settings you have set in config files ?
sm plugins list ?
Disabling nextmap.smx and mapchooser.smx only stop interfering CS:GO own
end of match map vote system, if you use that.