That's caused by missing events and that is by default, not the add-on. When an event is missing on the server it tries to resolve the event's index (the way the server sends client events is using a bunch of indexes and names on each index), so if your event was onActivate (0) > Player (0) > doStuff(6)
When you do not have the add-on it finds whatever the index was at "6" (I believe), which is something else.
To fix this, the server would need to make a workaround by registering the events it finds on each save.