In that case the error is either about calls to 'add_to_log' OR it is about handling events.
If it is the former, then the simplest fix is simply to delete the 'add_to_log' calls (not a great solution, but should get the plugin up and running again, without a long-winded process of replacing all the 'add_to_log' calls with event classes).
If it is the latter, then you (or a developer) will need to look at https://docs.moodle.org/dev/Event_2#Event_observers