I'm honestly quite frustrated. I'm having tons of issues with items in SP.
Basically, not only does the stash make the game crash randomly (deleting items in the process), but I've also found out that sometimes I'll pick up an item and it will not show up in my inventory, effectively disappearing instantly. This is terrible at the early game, but by mid/late game this is incredibly frustrating, as the only items you'll probably be picking up are SU/SSUs that you might find useful or valuable, and having them magically disappear makes the game borderline unplayable.
On another instance of the issue, I got to the Travincal council, only to find that all of the Khalim body parts had disappeared from my inventory, making me do that annoying quest all over again >_<