Can't Edit in Sculpt Mode After Un-Hiding Parts of Mesh in Edit Mode

I'm working through my first character modeling class, and having an issue! I hid the main body (anything past the wrist) of my character while in edit mode, to work strictly on the hand. When I went back and unhid the rest of the mesh, I stopped being able to edit the mesh in sculpt mode. I am able to sculpt the hand, but when I click anywhere that was previously hidden, it won't move! At first it wasn't responding in edit mode either, but now that seems to have been resolved after "unhiding" the mesh additional times, even though it was already showing up.

I tried this in Blender 2.90 and 2.91 and neither are working.

Any suggestions? Here is the file: https://www.dropbox.com/s/5uh7100zk0rkqc4/Character%20Modeling%20Tutorial%20DIKKO%20Beth%20Model%20Hand%202.blend?dl=0

It's the Mirror modifier that causes the glitch in Sculpt mode. Have a look at the modifier panel and you will see a warning message: "Sculpt: Hide, Mask and optimized display are disabled". That means the body is hidden but because hide does not work you still see it. A Fatamorgana ;-)
Press the little monitor icon "Realtime" right next to the Mirror modifier's name (in the modifier panel) to disable it in Sculpt mode and you will see what Blender sees. It's only the left hand visible.
Solution: In Sculpt mode, press Alt + H to unhide the hidden body.