I tested it with again with the monster addon and it throws hundreds of errors.
Script warning, "doomrl_monsters_beta_6.2.wad:D_AFSHKT" line 61:
Numeric type expected, got ""
Script warning, "doomrl_monsters_beta_6.2.wad:D_NCACOD" line 367:
Numeric type expected, got ""
Script warning, "doomrl_monsters_beta_6.2.wad:D_CSPIDM" line 908:
Unknown class name 'RLArmageddonSpiderMastermind' of type 'Actor'
Script warning, "doomrl_arsenal_1.05.wad:DEC_FIST" line 129:
Numeric type expected, got "None"
Script warning, "doomrl_arsenal_1.05.wad:DEC_CSAW" line 607:
Self pointer used in ambiguous context; VM execution may abort!
Script warning, "doomrl_arsenal_1.05.wad:DEC_FLAM" line 299:
Unknown class name 'RLFlamethrowerFlameSA' of type 'Actor'
Script warning, "doomrl_arsenal_1.05.wad:DECORATE" line 9843:
Numeric type expected, got "HEYSTOPTHAT"
It seems to be tied to the GZDoom version, since using 2.1.1 gives considerably less errors.