I am experiencing a bug in v1.20.8.2 in KSP 1.5.1 wherein any generator that uses ChargedParticles appears to be immediately deactivating with the log message "Generator Shutdown: No radiators available!" despite my vessels having several different radiators attached. (Vanilla, Interstellar Extended, etc...)
I believe this can be traced to line 1054 in FNGenerator.cs, but without a proper development environment set up for KSP Mods, I'm unable to test further myself.
Please let me know if any other information would be helpful regarding this.