We just shipped a hotfix that included a fix for player and humanoid creature models going permanently invisible, primarily in fractals. When the bug occurred, it would result in all future models failing to load and going invisible until a map swap.
This bug has been occurring for months, and we were having trouble finding a way to reproduce it. Thanks to clues from community reports, we were finally able to nail down a way to reproduce the bug consistently and thus were able to find the fix. The three key clues were:
It turns out there were actually two separate code bugs working in tandem with a particular skill and a specific timing, and that combination would result in the issue arising after repeated uses of the skill.
Please let us know if, after this fix, you notice anything else going strange with player or humanoid creature loading.
Thanks for your help in nailing this down!