Glitched Sculpt Won't Go Away

I was working on my sculpt and accidentally added another extra multires so I clicked delete higher, nothing happened so I changed sculpt and render level back to 5, and a part of my sculpt glitched out and as soon as I smoothed it out and saved the file, it reverted back to the glitched state and it won’t go away.

Here’s a video if a I didn’t explain so well: