Hi,
After a long investigation, we found the following situation on our Custom Board.
The value of PLLU_DIV seems to be normal if [CPU pin235:PMIC_BBAT] is high when the CPU is powered on.
In our board, we have an RTC battery connected to pin235.
When the RTC battery is connected, PLLU_DIV value is always normal.
When the RTC battery is not connected, the PLLU_DIV value is sometimes abnormal.
Finally, the our circuit has been modified so that power is always supplied
to PMIC_BBAT before powering the CPU Module.
So far, we have not had a USB -71 error in modified circuit.
This is the workaround in our case, not the official view.
If you solve it, please let me know what the cause was.