There are a number of recent changes to FitNesse that are in the edge, but not in the release, that might improve the behavior for you. I know that one feature directly related to the removing of CachingPage. https://cleancoder.ci.cloudbees.com/job/fitnesse/lastStableBuild/
I haven't tried this particular scenario, so I can't guarantee it resolves it. I also don't usually recommend running two instances out of the same folder structure. When I have done so, the second instance really only existed to view results of tests.