I think it was a moistureproofing issue. They didn’t handle things well when things got wet. At least that was my experience. Something somewhere would short/surge and poof. The resistor turned into a fuze.
I bought one once thinking it was the problem and it wasn’t. Kept it in the top drawer of my tool box for over twenty years. Might still be there.
Currently 2 of my boys own 1 77 slant six Aspen, 1 80 slant six Volare, and 1 318 v8 77 Aspen all with ballast resistors and none have blown since I picked up the first Aspen for one of them in 2001.