Import kerning groups from ufos

I have some masters in ufo format that I need to bring together in a glyphs file.
When opening the ufos in Glyphs, all kerning is flat although there is a groups.plist showing defined groups inside the ufo. Importing kerning groups via File>import>metrics is not fixing things.
For some of the masters, kerning classes appear in OT classes, for others it doesn’t. This and the classes names (_kern1, kern2, kern3 etc) is pointing to kerning done in FontLab, would that be the reason why stuff is messed up?
I may write a script to parse the groups.plist from the ufos to set groups in the Glyphs file, but before I do that, is there something straightforward I’m missing?

Are you sure the groups file contains kerning classes? Opening an ufo should take case if the classes. Can you send me one of the .ufos?

The problem is that the classes are in a very old and not standard compliant format as it was stored by old FontLab.