this things happens when i upload mesh that i edited via Blender.
using blender 2.81, and i just import and export into DAE(normal) and this always happenes.

any solutions please?

you can export as dae, but you cant import a dae, you must upload it with a normal viewer

Might wanna tick that Keep Bind Info when importing it in blender as dae this usually helps out for skeleton issues in dev kits and stuff that are .dae its on right side of the import menu, that way it uses the binding data of the original skeleton,in dae export tab has same button under Extra make sure u tick that if u use normal blender .dae export. Also in blender before u export press A to select all, then ctrl+A Apply All Transform, if u change position or change somthing on the mesh that way will fix the deformations of the mesh when u reup. Deformations on the mesh usually are caused cos location or scale or whatever u changed up is not applyed and what Lagertha said about correct viewer to reupload too is a factor. Anyway could be one of them things hopefully it fixes the issue for u x)

i'm using Firestorm viewer when try upload thing... but won't get better :(

thanks, i tried it, but it doesn't works either

Can you describe step by step when i should do that?

i mean, should i apply ctrl + a > all transforms before doing changes to mesh or after doing that?

dont reply use the @

Ensure "Keep Bind Info" is ticked on import and export.