I did add it to an existing project. Is there a way to disable the global restock timer? Otherwise I can try setting restock to -1 and see if that helps.
Viewing post in Trilobytes MZ: Limited Stock Shop comments
Setting it to 0 does disable it, but the problem is the code is still checking for it being there so whether enabled or not you'll still have this issue. It's because the object is created on game start, so obviously it doesn't exist in your save.
I'll update the plugin to create the object if it doesn't exist when it's needed. Should have a new version up soon, thanks for the report!