I only have some QoL mods and mostly building pieces and weapons, but most of them does not work with the updated game engine yet. Weapon-related mod that is not disabled is the javelins improved.
I also tried disabling all the remaining mods and the helmets were still there, still 49 (picture shows 48 because I dismantled one), and my materials were the same.
Probably @Multigun himself has some wise words for us!
Again, I somehow doubt it because Multigun uses IDs starting with 699xxxxx for his items from Javelin Improved. Anyway, he can take a look to re-confirm.