help editing model with blender? (broken after exporting to unity)

[Nyuu]

i am trying to edit a model i have. i have a project file for the avatar in unity already and i just want to edit the model slightly for a quest version. whenever i export the model from blender, and put it back into the unity project, the entire model is completely broken (polygons all jumbled and stretched random directions).
this happens even if i dont do anything to the model in blender at all; i can just import the FBX to blender, then immediately export it, and the same thing happens.

anybody know how to solve this? i can't figure it out.
I'm using blender 2.82a

[Doranos]

I would suggest to make a new Unity project (just for testing) and then put that model edited from Blender in it. If you don't get issues, then you are doing something bad while moving the model into Unity (could be overwriting problem).

[Fluffy]

So its a late answer so probably wont help you anymore, but for anyone in the future finding this. The most common reason I see what causes the above is not having the right export settings.

After you click export, under "Transform" > "FBX Scaling" > "FBX All" (can be another depending on project but that's the one I always use).

and for a little extra bone reduction in "Armature" disable "Add Leaf Bones"