The PLB DDR locks up during PLB Indeterminate Burst Read operations.
This problem has been fixed in the latest core included in the EDK 8.1i Service Pack, available at:
The first service pack containing the fix is EDK 8.1i Service Pack 1.
The problem appears to be caused by a memory refresh operation occurring on the last data beat of an ongoing Indeterminate Burst Read. When the DDR controller returns from performing the refresh cycle, it fails to provide the final data and data acknowledge to the IPIF. This situation leads to eventual system lock-up, requiring a reset.