I’m 100% sure for Venezuela and could find you the source, Europe said they didn’t have time despite being asked more than 6 months prior to the elections(, and still having 1-2 months ahead of them).
For Syria i’m almost certain, but i think that i could find the same for Cuba, probably Zimbabwe and in any case i’ve read such suspicions about Russia and Iran, we even showed videos of a ballon in front of the c.c.t.v. for Russia, even if the surveys proved that V.Putin’s support was/is legitimate, on which country would you like sources ?
In general, every government qualified as a “regime” is considered as cheating at elections, i don’t see an exception.