Thanks to Phil Guiet for finding this bug and providing me with the Kicad files to track it down!
I was unaware that you can change the layer names in PCBnew. Well, I knew you could change the layer names but I wasn’t aware that the file structure would carry those names instead of F and B (Front and Back).
Therefore if you changed the top and bottom layers to something other than F or B RenumKiCadPCB would crash – which is never good. Now the software keeps track of which layers the modules are on, regardless of name. And it should no longer crash.
This is the link to V0.204 (source, manual, and a Windows EXE) RenumKiCadPCBV0204
Please let me know of any other bugs.