My M4-A1 has been working fine for days. I detached the magazine to reload and suddenly it wouldn't allow me to reattach the magazine. Exiting the server, reconnecting, changing servers, closing the game, and validating local files did not correct the problem.
I tried replacing all other attachments, each of which worked fine, and I tried using a different magazine which also did not work.
The gun shows that it has a magazine when viewed in the game world, but when viewed in the inventory it shows no magazine attached.
It allows chambering a single round and shooting, but otherwise is no longer functioning as expected.