Areas of the mesh are being removed when trying to use Sculpt/Dyntopo

Hi, I’m trying my hand at creating characters using the sculpt tools in blender but I’m having issues as for certain points my mesh sometimes will stop reacting to the sculpt brushes and will start removing parts of the mesh instead (sometimes outright deleting parts)

Does anyone have a solution or workaround for this? (also any general advice about sculpting would be appricated, I’m quite new to this)

File Link: https://easyupload.io/4dftm5