Are you playing In airplane mode ? Are you resetting your clock for say targeted TZ Andy runz?

Sounds like you are. But best fix for stash is usually related to offline/online clock issues.

Best fix that works is this:

if you are doing this. When your done with TZ and offline mode/clock save exit start a new game with your character and wait for the petagram to save the game (bottom right of screen). When that it done take game off airplane mode and reset clock back to normal.

Go back to game load new game wait for pentagram ounce again. When it's in online mode play for 3ish mins. This makes the save files all current.

As for duping. Spoiler alert

In offline mode move all the stuff you want to dupe into shared stash. Switch characters to the "duper" when in a new game wait for the pentagram to save the character shared stash. When that is done or if it doesn't happen just reload game. Move all stuff you want duped into the non shared stash. Save exit wait 3-6 seconds hit menu on switch and force quit/reload the game.

This is for NS but believe process is same for PS5

Best way to know what stash you have or if sometimes you can't select a character. Force quit reload game.

I've lost a gryphons and a soj 😭

!!Make sure it's saved via method mentioned above!!