Got a nice glitch where occasionally when you pull up pipboy you just end up staring at blurry ground - as if your arm and pipboy are invisible. Happened a few times so far, restarting the game solves the problem. Ironically, first time it happened is when the character goes through the special animation of pulling it off a skeleton when you first acquire it. I hit E to pick it up only to get a floating blurry screen for a while.

I've had that bug as well, it was also accompanied with a disappearing weapon. Oddly, the interface and shooting still worked, it just didn't show any view-point model at all. For me, besides restarting, it also fixed itself after using a crafting station (probably because that triggers that short third person sequence of you starting to work at the station?)

You don't happen to have a stealth armor part ? I picked up a legendary that gives me enhanced stealth when not moving and every time I crouch and stand still my character turns into your traditional videogame stealth silhouette. If I bring up my Pip-boy while in that state the effect remains making my Pip-boy invisible.

Next time it happens, try switching to third person mode, then back to first person (Back button on 360 controller, V for keyboard?).

Started the game last night. Happened to me once, and swapping first/third person seemed to fix it.

This happened to me as well with both the Pip-Boy and weapon disappearing. Happened after I picked a lock. I just reloaded a save as I was nervous about creating any broken saves with it gone.

As pointed out earlier, you don't need to restart or load a previous game. You just need to move to 3rd person view and back into first person view (for PC users, scroll the mouse scroller).

I have this same thing. I was so happy to get that piece of armor because I'm playing really stealthy but now I don't know If I can keep using it. So annoying to never be able to pull up my Pip Boy while sneaking.