[NaS]

There is a wrong Object ID attached to the player, maybe an old script with a deleted ID? Or try looking into the script and find the line, where it creates the object, then lookup the object ID for the helmet you want there:

https://sampwiki.blast.hk/wiki/Samp_objects

EDIT:

Oh sorry, didn't read that others have it.
Do you see the other player's helmets but not your own, or do only THEY see all the helmets?

If only they see the helmets try to reinstall SA-MP, maybe the SA-MP.img or something else is broken, or missing.