The points at which the game transition between acts seem a bit arbitrary (mainly for Act I to Act II), and I don’t see a narrative or mechanical reason to lock us out of previous maps and quests. As far as I remember, previous Baldur’s Gate games didn’t have this kind of points of no return. Why do you think they did it? Do you like it?
Does your DM straight up not make it clear there are time constraints, either through context or by just directly telling the party? The story in BG3 emphasizes a time crunch in one thing, that doesn’t matter until you progress beyond certain map points, but then you get these other couple of quests that make no effort to say there is any time limit, so you rest after 1 fight and fuck everything up without even realizing wtf happened. Even after it happens, it’s not clear it was because you rested and time had passed. From the player’s point of view they were in a dungeon, rested, woke up and all the bad guys were gone/dead and the quest gets stuck with nothing in the journal telling you what happened. It appears to be a bug, but it’s actually an intended consequence that is never telegraphed or alluded to, period.