Hey,
I did the only other thing remaining I could think of, namely trying to convert the project from 4.13.2 to 4.15.1.
I opened 4.15.1 then imported a COPY of the project in it.
All that was left to do, was updating the plugin files to 4.15 - which I was able to do for almost every plugin.
Since then, I’ve cleaned up assets and compiled anew.
Voilà - packaging and running works fine!
Although I still have no idea what caused the problem, this (stressful) workaround worked fine =)
Cheers,
Abaris