New iPad Pro 11" not recognizing USB Midi

i have several synthesizers (eg korg minilogue, arturia microbrute, behringer poly d). their usb midi is connected via some hubs, so i can record and control them with my ipad, via audiobus or cubasis. using my old ipad pro 10.5" or my iphone 11 and the apple camera adapter lightning to usb, this works great.

now i have a new ipad pro m2 11" with usb c connection. using the original apple adapter usb c to usb a, this setup does not work anymore. the hubs obviously are not recognized, so no instruments show up in neither audiobus nor cubasis. connecting single instruments individually works tho, so the hubs definitely are the problem.

i do not understand why these hubs worked with the (supposedly more restrictive) lightning connections, but not with usb c.

what can i do to make my present setup work again (without buying new hubs)? any ideas?
thank you!

ipad pro m2 11" 256gb
latest ios, ipados 16.3.1

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