The mixbusses can't be directly sent to AES50. You have to send them through either the Out 1-16, Ultranet (P16), or Aux out tab first.
Here is canned response to the X32's routing flexibility.
Routing is one of the most confusing aspects of this mixer. Because it's powerful, it's a little harder to understand the concepts. The output assignments are generally done in two stages. Output 1-16 is main "staging" area to assign individual outputs from the many different sources (Aux Out and Ultranet can do the same). Output 1-16, however, is only an intermediate stage; these assignment go nowhere until they are then assigned to Card Output, AES50 A/B, or XLR Output.
I have a video on this subject. https://youtu.be/hWPCKCSR7fU Maybe this will help.
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