Sorry, but I have no idea then. I'm unable to replicate this at all. You can try the discord server to see if anyone else has a similar issue and try to isolate a cause.
A couple of last things I'd try as a sanity check:
- Actually extract the jar file and look under unthemedweapons/campaign/rulecmd, there is a wpnxt_CacheDefenderInteraction.class there, yes?
- Make sure you don't have another folder in your mods directory with a mod_info.json having the id "unthemedweapons" -- e.g. if you downloaded the source code and extracted it to your mod folder at any point in the past, that folder could possibly be overriding the actual mod folder.