CDJ2000NXS2 "matching" list is empty

2 CDJ2000NXS2 players, latest firmware (1.72) connected directly together with LAN cable.
Link works correct, I can browse music from the other player via SD/USB.
When pressing shortcut - matching I see the track playing on the other CDJ but the list is empty, no results.
All music is analyzed in RekordBox (latest version 4.5).
I use Mixed in Key to analyze Key and write that to the "Initial Key", this has worked in the past.
I also tried new files without MIK and importing directly to RB but that doesn't seem to make any difference.
Also tried different USB sticks, same result.

In RekordBox itself I see results in "related tracks", I would expect the exported files to USB would give the same result on the CDJ's for that track and related tracks.
The "traffic light" system works, I see green/matching keys in the browse list on the other CDJ.