It makes sense, the iPad Pros graduated to using full blown M series chips so the A Pro chips they used to use can filter down the stack.
edit: oops I mixed up A Pro and A X
edit: oops I mixed up A Pro and A X
Apple used to use the X suffix for bigger versions of their phone processors that went into iPads (starting with the A5X); that went away when the M-series was introduced.
And the "Pro" suffix itself doesn't seem to denote anything in particular-- there was never a non-Pro A17, and the "A17 Pro" going into the iPad Mini is itself a cut-down version of the chip that went into the iPhone 15 Pro (it has one GPU core disabled).