Hi,
I run the A4 as slave of the OT without any problems.
A4 in Global - Midi Sync clock recieve = on, transport recieve = on and progr ch recieve = on.
In Midi Port Config all midi inputs = midi, recieve notes = on, recieve CC/nrpm = on, live rack on track = on
midi channel …prog ch in on e.x. 7 or higher (not 1-6)

OT: Function + Mixer - Midi sync - Clock send = on, Transport send = on and prog ch = on, Channels = Auto Channel > 8…

…and it works in perfect harmony.