I've experienced rim lock twice in my P32, both times using Fiocchi 73g FMJ ammo. In both cases I suspect a round was just a mm or so short and I didn't catch the small difference as I loaded.
Once rim locked, there is nothing you can do. The slide won't move and the mag won't eject. Your only option is to remove the sole plate of the mag and drop the spring and remaining rounds out, then you can remove the mag and release the slide. Not something you would ever want to encounter in a defensive situation, obviously.
I load a 60g Gold Dot in the chamber and second round, and the rest 73g Fiocchi FMJ. Since the rim locks I'm very careful how I load each round and also check each round for length.