Might be a conflict with another plugin that touches events. To confirm, try the following:
- Create a new project
- install and activate ONLY the Field Skill Plugin
- set the plugin to show in the menu, don't change anything else
- Add <FS: RESTORE_ENABLED> to the Notes of the map
- On the fresh map, place a treasure chest with some content
- Start the game. Open the Chest. Try to restore.
If this is working, it's either a setup issue or a plugin conflict. It's a bit hard to debug remotely. If the issue still happens, try opening the console while the game is running (F8) BEFORE it crashes, and then post the crash error message in full here.