I've found something : in the import list of the new version, choose at the end of the list "Formated CSV", (I've tried everything in the list...) hopping you do not had the idea to export your last saves in the txt format. The you'll have to check every link to be sure each have the connection url, if not, enpass won't recognize the connection form. With this new version things are in the wrong place once imported and you'll have to correct everything one by one.
It would have been usefull to precise this....BEFORE users install the update to avoid all this mess. If I had knew this before, I wouldn't have updated for sure.
Anyway, thanks for this extra-work...always fun to loose time huh ?
PS : for the record, in the meanwhile I had reinstalled the previous version = 5.6.9, but one I restarted my browser, the extension didn't work...because it was a 6.0 .xpi and not the 5.6.9, so as said in the FAQ incompatible. It would be nice to give users who do not want to migrate, (at least for now) the old xpi so that they wouln't loose time....