... and by forever, I mean FOREVER.
I didn't understand what was causing this until yesterday. After testing it, I am certain that killing an enemy who is frozen by a 'Freezing' weapon, will cause them to stay frozen even when they respawn later.
Unfortunately now I've got many high level areas in my game where half or more of the enemies, even after death and respawn, are stuck in suspended animation. Nothing I have tried can break them of this affliction.
I've tried console commands (kill/resurrect, disable/enable, recycleactor). I've tried freezing them again without killing them, and waiting for them to thaw. I've tried shooting them with Syringer Lock Joint darts. I've tried altering the freezing effects in FO4Edit. Nothing I've done can free these poor souls.
EDIT: There are at least 3 threads on the FO4 Steam Discussion board about this problem, so I know I am not the only one experiencing it.
At this point, I am more concerned with fixing all the broken NPCs in my save game, than fixing the broken legendary effect. It's easy enough to stop using the gun... but all the permanently frozen NPCs kinda ruin the game. If anyone can figure out how to snap them out of it, please let me know.