JabRef won't spawn menus

[ExecutorElassus]

So, I'm asking (to start) for tips on how I'd even debug this. Context:

JabRef is a standalone java-based bibtex database manager. I've been using it for years with no issue.
However, after a long hiatus, in between which FVWM switched to using XRandR to manage screens (previously it used xinemera, I think) and thus now explicitly treats the two screens as separate, I can't get JabRef's menus to spawn. Like, the "File," "Edit,", "Options" menus at the top. When I click on one of them, nothing happens.

When I start JabRef from a console, nothing shows up when I click the menus, so I'm not getting any console output either.

So, how do I go about figuring out what the problem is? Since JabRef is a standalone program, I'm not sure what options it has for logging, etc.

Thanks for the help!

EE