Strange artifact in model (Maded in blender 2.9)

Hello friends, my model has strange artefacts in it hands can anybody explain how to fix it? Thanks in advance. If you need export and import settings screenshots they in this question Imported animation smaller than actual model (Maded in blender 2.9) - Character & Animation - Unreal Engine Forums .
This how it looks like

I solved this problem. In my case i using “mirror” modificator on my limbs and it was wrong. The true way to dublicate your limbs without any artifact in UE4 is: highlight limb to duplicate - Edit mode - again highlight limb - press “P” - by selection. if you know any other ways to solve it simplier I will be glad to advice