I just played a session and noticed that saving didn’t work properly anymore - I would enter a save name and hit save, but afterwards, the save would not appear in the list. When I tried to reload the last appearing save in the list, the game told me it detected save corruption and could not load it. After the initial wailing and gnashing of teeth, I noticed that the last save in the list, the corrupted one was right after some milestone. I reloaded the last working save, played up to the part where that corrupted save would have been and noticed that it was right after some cutscene where the game would have been autosaving WHILE I initiated the quicksave. It seems that you can royally screw yourself if you cause overlapping save procedures, so for the foreseeable future, I will make sure that the only one initiating saves is me, no more autosaves here.
tl;dr: If you save while an autosave is being made, your save will risk being corrupted. Generally don’t overlap saves in progress.
How did the 2 saves at the same time even happen? Normally, BG3 blocks all further saving while a save is already in progress. Managed to skip an autosave trigger like that before.
The save process is usually initiate save (f5 or via menu), then the noticeable part where you can’t move or do anything, then you can move your characters again but if you hit esc, the buttons “save” and “load” are still greyed out. I assume that this is the interval where shenanigans can occur. A few seconds after that, the buttons become usable again and the “saved successfully” message appears on-sceen.