After all this time finally?! The bug is where you apply many appearance cosmetics on your character, and upon zoning to a different area or traveling to somebody, it'll disappear.

The catch is: It's actually still equipped, you just can't see it, but everybody else can.

The fix is: Not putting more than 5 appearance options on your character. So a maximum of 5.
Source: https://forums.elderscrollsonline.com/en/discussion/comment/3533291/#Comment_3533291