Parts Of Object Hidden, Cannot Be Sculpted When I enter Sculpting mode, I found some vertices cannot not be sculpted.


I switch to edit mode and I found these vertices are hidden (?not sure).
I can press Alt +H to unhide these vertices. But when I switch back to sculpting mode, these vertices still cannot be sculpted.

Switch back to edit mode and this part is still hidden. (like fig.3)
How can I make these vertices available for sculpting?
What kind of function make this situation?
This recently happened to me and I believe this is a glitch. When I switch to tab mode I tried to reveal hidden Alt+H  the vertices. When I switch back to sculpting mode, I can't sculpt it.
Again, I believe this is a glitch. I tried to copy the mesh to 2.83 version, unhide the vertices, and copy it back to 2.9 version and it worked.
Edit: after that, whenever I add a mask the it will be invisible. I think it's a bug