I was having difficulty with JabRef throwing up “unhandled exception” errors when attempting to copy and paste anything, especially when copying BibTeX from elsewhere (Google Scholar) and trying to create new records. As well as multiple errors half of whatever I was trying to paste would disappear. So I uninstalled it and downloaded 5.1 from the “master” directory, using the .msi installer. So far this version hasn’t thrown out any errors. However, it does not run when I click the .exe or the default entry in the start menu.
For the moment I have resolved this by creating a shortcut to the .bat file in C:\Program Files\JabRef\runtime\bin in the Start Menu directory. But I wondered if this is a problem with my setup or with the 5.1 version for today (27/08/20). I’m using Windows 10, just to be clear.