This is UNQUESTIONABLY the cause.
When you switch away from any weapon it begins reload.
If you come back to that weapon before it’s reload time is complete, you need to wait for the reload to finish, you just don’t see the animation for it.
@Plaff Not really a bug, but maybe poorly communicated.
I should also note it’s this way for ALL platforms, not PS4 specific. But… it’s not really a bug, it’s middle of reload. Perhaps they can make it pull the weapon up into that % of reload complete so you see the reload finish on screen? Or they could just overlay text “reloading” or something like that…