Hi,
I have seen many issues with Astell and Kern on Interact and have some myself. But it is strange that with the older MC versions I had less problems with my AK240. Later I also bought an SP1000 and recently the old AK380. They all have one identical problem, but the SP1000 is a bit less problematic. That user interface has changed but it is still Android.
When the AK player is fresh and empty, or just formatted it is (only) recognized by the 32 bit version of MC. It is then possible to tranfer music to the player. But in my situation MC crashes very often during the filetranfer. I mostly use ape but have also tried flac but that does not make any difference.
Somewhere along the file transfer something happens, mostly after the MC crash.. After that syncing with the AK player becomes problematic. Songs which are already on the AK player and are still being synced result in an 'error' message in the detailed transfer screen. The normal behaviour is that songs which are already on the player are not synced again.
So when I add a new song to a playlist on the PC the sync will try to sync all songs in the playlist which results in an error message for all songs minus the new one. The playlist will not be updated with the new song or order of songs. The new song is properly transferred to the player, but not selectable via the playlist.
From this moment on the (temporary) solution is to format the AK player. The formatted player will be usable for a while, until the above happens again. Somehow the communication between player and MC is not correct anymore. Deleting the playlist from the player does not help.
I hope that one of the JRiver engineers can do something with this info. I can provide additional info if needed, just let me know what.