The only time I have had problems with the PS5's rest mode is when we have had powercuts, which is extremely rare and has only happened twice since I bought the console at launch. I have been playing Spider-Man 2 all week resuming from rest mode with no issues.
I always hate the way the PS5 complains about not turning off the console properly then proceeds to give you a stern warning not to do it again before it runs through the drive checking routine. It's not like I do this on purpose, Sony! Also, my Xbox Series X never does this and is just happy to boot up post-power cut with just a slightly longer initial startup complete with Xbox logo.