This is caused by improper throttling of the underlying NPI interface, leading to NPI/MCB FIFO underruns.
For errors resulting from writes, a patch is available for download at the end of this answer record. To use, extract thezipped patch to the EDK project pcores/ directory, and restart XPS. The MPMC is currently not planned to be updated to include this patch.
A similar failure has been observed for read transactions, but there is no patch currently available.