Cool, was wondering where they went.

(edit: tried to fix but they still don't show up, is there anything else I might have missed?)

I noticed that too. My most recent game doesn't have a thrumkin tribe. A few weeks ago it did. I didn't mess with the faction settings. Activating Faction Discovery doesn't list them as an option.

I modified the mod xml directly to add the _ in the DefName.

I started a new game a few days ago and I have the Thrumkin faction on the world map (only 2 but they are there).

I noticed that the _ was forgotten because while translating the mod, the space was generating errors.

You should really have mentioned that this is a scenario def.