This has happened to me and others when we play online together. Occasionally, (maybe 1 out of 5 online sessions) The entire HUD disappears when zooming in on a scoped weapon. Zoomed out is fine, but everything is gone when zoomed in. I have taken screenshots in the game of the issue. The friends I play with have experienced it too. I was surprised i didn’t see it mentioned as a bug yet. (Along with all the other issues). Also once in awhile something causes the player to start running very slowly for several minutes, but it usually sorts itself out. This has also happened to all of us that play together. Restarting the game will fix the scope issue. I have been holding out on playing TPS because of the major bugs it has. I’m pretty disappointed.
I recently had issues with the running slowly issue in TPS. Turns out, I was using a weapon called Frostfire. It’s similar to the Chulainn SMG in Borderlands 2. Frostfire deals both fire and cryo damage, but has a chance to freeze you when firing. This effect can sometimes pass on to other weapons and will persist even if the weapon is unequipped. Lasts until restart. Chulainn deals shock and slag damage and occasionally slags the user.