Conspiracy (Diplomacy Android app) possible bug or rules misunderstanding?
Indeed, there was a problem with the resolution engine to manage this kind of situation in Conspiracy.

I've worked on it and it's now fixed. From now on the server has been updated and all the next resolutions will be managed correctly. In application side, the analyse engine will keep displaying this error as long as players are using the version 2.9.0 and lower. I invite anyone to update their application to the new version (v2.9.1), it's available in the PlayStore from March 21st 2020.

Thank you for reporting me this problem.

Here are screenshots that show you how things is now managed :