Stacking under Frodo not working as in Eden

In my movie library I have one folder with multiple movie files named like this:

Pixar.Short.Films.Collection.Vol.1.720p.BluRay.x264.[PART1]-The Adventures of Andre and Wally B (1984).mkv
Pixar.Short.Films.Collection.Vol.1.720p.BluRay.x264.[PART2]-Luxo Jr (1986).mkv
Pixar.Short.Films.Collection.Vol.1.720p.BluRay.x264.[PART3]-Red's Dream (1987).mkv

Then there is a
Pixar Short Films Collection Vol.1.nfo
together with cover, fanart, etc.

In Eden, those were correctly stacked as one movie, but in Eden each mkv appears as a separate movie. I can not find a clue in the help why this is not working anymore. Can anyone provide help what has changed and how the names need to be changed?