Completely solved.

Conclusion: I'm an idiot sometimes. :D

in the wardrobe is the box checked or unchecked next to "Only show items you own" ?

I thought it was checked, before, but it's not, now, when I look at it.

it needs to be checked because you can only wear items you own. Hope that helps!

- And here I thought I'd checked EVERYTHING... The facepalm is real. Clearly I don't keep the best track of which items I own or don't. Goodness. Two days of self-made nonsense.

I just tested it, and was able to successfully save with an avatar that shows up. Someone delete my existence from the last two hours, please. Ahem.

(Thank you, so much!)

No worries :D You're welcome!