So, we've had reports on xen-devel which look a little like this.
@BlueBadger are you able to switch back to your 7950x and try booting Xen with
x2apic_phys=true ? It appears that the -X processors are missing a feature in their IOMMU and Xen was getting confused when setting up interrupt handling.
https://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=0d2686f6b66b4b1b3c72c3525083b0ce02830054 is at least part of the fix, but so far feedback on the mailing lists suggests it's not a complete fix.