I had a lot of issues going from PS5 to PC and back again in the beginning. The way I finally got it working is to disconnect all devices on Larian's network, then relog them in.
From there, whenever I want to go back to PS5 from PC, I open both versions of the game. I then load into another character or older save on the PS5 and then do a fresh save on the PC. Then, check to see if the new save is showing on the PS5. If it is, great, your'e done. If not, close and reopen the PS5 version and it's usually there.
Once you get them seeing each other both ways, it crosses save pretty consistently.
