Why doesn't Rekordbox 6 recognise my XDJs via USB - Rekordbox 5 does?

I have two XDJs Mk2 connected via USB. With Rekordbox 5 open on my machine I go to the physical XDJ and then select Link > Control Mode XDJ, and then click the button.

I then cannot choose which Deck i want to control when using RekordBox 6.

If I follow the same procedure with RekordBox 5 - everything works fine. I control Rekordbox from the XDJs.

I have updated firmware, reinstalled drivers and Rekordbox, copied the permissions for the Applications.

What next please?