You may find UnsupReq, NonFatalErr, and CorrErr status asserted after power cycle or operating system (OS) reboot when using the P-Tile Intel® FPGA IP for PCI Express.
According to the PCI Express Base specification revision 4.0 version 1.0, during the enumeration of a non-existent device or function, completion with UR status is sent, and UnsupReq is asserted. Meanwhile, Non-Fatal Advisory Error is determined, and CorrErr and NonFatalErr are asserted.
To work around this problem, clear the UnsupReq, NonFatalErr, and CorrErr statuses in the PCI Express configuration space registers before checking them during data transactions.
This problem is not planned to be fixed in a future version of the Intel® Quartus® Prime Pro Edition Software.