Skeletal mesh invisible in mobile preview ES2

Hi,
So I am having this problem recently which is skeletal mesh invisible in mobile preview, I have looked it up online and all every solution I found is related to bone numbers, all of my characters are not exceeding the 75 bones which as far as I read that it is the limit, and my vertices are way less than 65k

These are my characters:

281166-1.png

281167-2.png

Note: everything else is working just fine and have no problems, my only problem is with my characters…