I'm looking into it right now. Are you using space age? I don't know what's causing the issue yet but I have a few ideas.
Does the military-4, rocketry and kovarex techs all show up in your research tree? It's possible to be unable to click on advanced nuclear weapons if you haven't yet mined the uranium required for the uranium processing research. In 2.0, some researches are unlocked by means besides research labs.
The prerequisites for advanced nukes in both vanilla and space age is: {"military-4", "kovarex-enrichment-process", "rocketry", "atomic-bomb"}. This seems redundant since "atomic-bomb" is {"military-4", "kovarex-enrichment-process", "rocketry"} has the same perquisites and, while I couldn't replicate the issue, changing this might solve at least some mod-conflict related problems for some people.
I played a non-development mode, non-cheat space age save to the point where I could queue advanced nuclear weapons research.
So tl;dr:
- make sure you have uranium-processing researched
- find out if all 4 of the prerequisites are showing up in your tech tree
Let me know if it's still broken after checking that stuff and I'll push an update that removes redundant prerequisites and see if that fixes it.
