I am running into the same issue. I have a Ringedge 2 multi being used by a pair of Vewlix. When cabinet 2's JVS board is connected to cabinet 1's JVS board, only controls for cabinet 2 work (and reads as player 1). When cabinet 2's JVS board is disconnected, cabinet 1 controls work just fine.
I am using the Taito JVS board (K91X1147A) in both cabinets, with the Taito VS kit (K91X11151) splitting audio, splitting video, and passing through the JVS to the second cabinet. Is this a compatibility issue with the Ringedge 2, does it require Sega JVS boards to support the 2-cabinet JVS setup? Or is there something else I am missing?