Hi, I have the same issue with OP regarding save files.
I was playing with AI's, the game just crashes out of nowhere (which isn't the issue of this ticket), I got used to it and just made the habit of saving from time to time but then the absolute worst just happened. At the point where me and the AI's have uncountable units, the game won't just save the match. Auto-saves, saving on empty slot, cloud save, and overwriting a save file all don't work. I'm actually not sure if it can't save or if it indeed saves and I just can't access it. Because I noticed that there were 2 different sets of save files when saving but I just ignored it 'cause I thought it was just a kind of a display bug and that my saves would still be there regardless. As a result I tried deleting all the save files and saved on an empty slot, but damn I shouldn't have done that because I just lost my 140+ min match because it still did not work. I can't find the 'other' set of save files which I assume my match was located on. Now I'm not sure anymore if the the issue is saving or loading but nevertheless the entire match was gone. It felt so devastating to lose all those time and effort. I think it had to do with the processing complexity due to number of units? There were 4 Insane AI's in that match and I was stacking my units until it filled up a portion of my base resulting in a really really big overall unit count. The game doesn't crash due the number of units, the issue is that it just fails to save/load.
Some more things to note:
I notice the game SOMETIMES crashes when trying to upgrade tower, skipping a cinematic (those in the campaign), and when zooming out to group very large armies where it goes to that strategic map thingy and then zooming back in to reality. Also sometimes upon loading a match, the camera 'forcefully 'pans into one of the corners of the map all by itself and can't control it anymore.
Oh, I already did what you asked OP to do. Just leaving a reply here to raise awareness (: