Hi, I am having this problem and is driving me crazy
I am sculpting a Character and needed to hide the top of the head so I can Weight Paint the inside of the mouth so I can move it to add details because I am an Idiot and I sculpted a closed mouth.
https://imgur.com/a/YDqBnvu (You can see the Tool flat not interacting with anything)
So after using both the [Hide Bounding Box] and [Hide Mask] and finishing the basic weight paint, I wanted to see the rest of the head, but I couldn’t, I tried many things, [Alt + M] to erase the mask then [Show All], Going into [Edit Mode] then deselecting Everything, and using [Show All], and many more combinations, the thing that did the trick was a weird combination of steps,
Alt + M To clear the mask,
Ctrl + I to invert the mask,
Show All (I noticed that when doing this steps the Tools actually recognized the mesh as being there but it wasn’t showing)
Show Bounding Box (Selecting everything I wanted to show),
Ctrl + Z,
https://imgur.com/a/z2hYtcq (Images of the Process)
Following this steps I was able to force the viewport to show me the mesh.
Am I doing something wrong?, Or is it a really weird bug that only happens to me because of my poor life choices and my inexperience with blender (This Is my first time sculpting a character), I searched the internet for something similar or a solution but nothing