someone take a look at my mesh?

the problem is that your skirt mesh has uv map only from one side, that is the reason why the triangles are showing...the easiest solution is just to solidify your skirt

first in object mode select the skirt and go to modifiers:
imgur.com/a/uIv5Kxb

then add modifier-> solidify:
imgur.com/a/LVdAYBb

Change the values and push apply
imgur.com/a/DW6psWn

import, and the problem should be gone, hope it helps