Q:

Why am I suddenly a UUID? 

I've had an account on Photo. SE as myself, cat for probably a few months, but today I opened Photo. SE from the HNQ and found my username to be a25bedc5-3d09-41b8-82fb-ea6c353d75ae, even though the rest of my profile on here matches all other SE sites.  
My bio and github link are correct, but my profile photo and name are wrong, even if I click "Save and copy changes to all SE sites" on another profile.         
I could in theory just update my name and profile photo here, but I'd rather have what I think is a bug fixed. 

A:

There was a bug all over Stack Exchange causing display names and avatars to be reset randomly. 
It turned out to be related to the mobile app, and was fixed back in July. 
Your profile here was probably messed up before July and you noticed only in October (the fix wasn't retroactive, i.e. those affected needed to manually change name and avatar.) 
Since it's now fixed, it shouldn't happen any more.