Unknown Technology is reseachable (yellow background) but unlock condition is not visible. Is this intentional?
Could it be Castra (Enemy research) or Discovery Tree (tech double hidden) incompatibility?

Did you update to 0.69.34? I messed up the release for 0.69.33 accidentally, so if you downloaded in that 20 minute window, it is definitely not working. Sorry.

Actually, do you have Discovery Tree installed? That one can probably mess with Rubia.

I see that Discovery Tree has an incompatibility with my mod, but from my testing, it may not work normally, but it should still let you progress. I suspect the issue is still working off 0.69.33 (which I am deeply sorry for).

I am reaching out to the Discovery Tree creator to see if he can add an interface to allow our mods to coexist.

At any rate, thank you for your report, and thank you for your patience. Let me know if updating your Rubia fixes the issue (in which case I can close it out).

It disappeared, thanks.

Looks like tech disappears after game is reloaded and comes back after a while. Could it be Castra effect?