I'd add that for over 5 years we've advised plugin developers not to fork (copy-paste and edit) official plugins/behaviors: https://www.scirra.com/forum/please-do-not-adjust-official-plugins-or-behaviors_t71650
This is because we've always known doing so causes all sorts of compatibility problems, just like the one in this thread. Other difficult compatibility problems that can happen include bugs being fixed in the official addon but not the fork, new features being added in the official addon but not the fork, and in the long run, the official addon gaining the same features as the fork therefore making the fork redundant, but leaving you with the awkward job of removing the fork from your project and recreating all the events that use it.
My advice to users would be avoid any third-party addons that are based on a copy of an official addon. You're basically signing up for these compatibility problems.
I am happy to work with addon developers to come up with alternative extensibility options, but I rarely see any discussion of this - most addon developers ignore our advice and fork official addons anyway. To try to avoid the problem in C3 we've done our best to hide the addon source code so it's simply not an option.
I would also add I appreciate all the work addon developers do, and it's great for the community. I only make an exception for this specific case of copy-pasting an official addon and changing it. I wish people wouldn't do that.