on all Profiler models it is totally clear which connector is host (='A' socket) and which is device (='B' socket)
An USB 'A' <-> USB 'C' cable explicitly codes the 'C' side to be the device side (note: it has to be a cable which supports datatransfer, and not only a charging cable) The Morningstar seems to recognize this correctly, as it starts acting as a device, but acts slowly as I understand from your reports?
Maybe the Morningstar has problems processing the MIDI data it is receiving *from* the Player, when acting as a device? For example: initially the 'Paintaudio' controllers had this problem too, and it was fixed by Paintaudio in their firmware.
The cable is a data cable. The Morningstar has two USB-C ports. One labeled "device" and one labeled "host." The Morningstar "device" port does work with the Kemper USB-A port. The Morningstar "host" port does not. Maybe this is expected behavior. If so, it is possible people are plugging into one or the other port unintentionally?