I was on my way to create an homebrew feat for the Leonin race on the Homebrew creation kit, and when I needed to pick a race as Prerequiste, I wasn't able to find Leonins in the selection.

More than that, I validated another race to see if it would be a minor issue and allow me to find it by editing the prerequiste after that, but now it also include "light armor", or "intelligence", in a selection for "Race" prerequistes. Is it a known issue? 

Beside, I hope that I'm posting in the good thread...

up, still can't pick the race

Unfortunately, not all races are accounted for yet in the Races dropdown for feat prerequisites, including Leonin. I don't know the reason why.

Edit: After some investigation, they seem to be missing races from the non-standard D&D sources. So like the Magic the Gathering-based sourcebooks, adventure modules (Fairy & Harengon), the non-core Locathah and Grung, and Critical Role (Pallid Elf).

Well, they were here for a time, as I managed to find a feat with the same prerequisite in the public homebrew. Is there a way to bypass this difficulty? Or would they be back soon?

Huh, they were? I've noticed some other things being changed with the site over the past day, so maybe they'll be back later.

I hope so, I'm really excited to get some feedback on it ^^ For now I just can't make it public yet --"

Updating it, as it's still not showing the leonin race

Only the races that already have published racial traits in Xanathar’s have their races as available prerequisites for racial feats you can enter the name of any race and skip the second part of the prerequ and it will display that race name but not be able to enforce the selection on a character sheet.