Hello Tommi,
If Java Monkey does not show anything, than the issue is with the Java Access Bridge (JAB) interface rather than anything to do with Blue Prism. If Oracles own JAB testing tools don't work than there is little we can do.
There are two possibilities:
1. You need to install a different version of JAB to be able to interface with the application or manually install if the application is using bespoke JRE folders. There is a lot of help in the knowledgebase about this - but my starting point is usually to get the client to reach out to the application vendor to find out more about the version of the JRE they are using and exactly what JAB version the need. Modern applications should be accessible so the vendor should know how to get their application working with accessibility tools.
2. If the application vendor has created their application in a way that is not accessible and is not complient with the requirements of JAB - then you will need to use Surface Automation techiques to interface with it.