I've noticed a pretty serious bug with how Arcade or possibly Arc Pro lints attribute rules. If a non existent table is left in the code (even as a comment) it will fail to save the rule.
This is definitely unintended behavior because the Expression Editor validates the code just fine (as in it ignores possibly invalid code in a comment block), but when the validation on save is triggered, it gives the catchall "Something Unexpected caused the tool to fail" error.
Attached is an image with some code examples: