I think your motherboard has failed.
Your PCI bus slots are wired to an 8 bit parallel data bus. The basic way to constantly monitor this is to add a nineth bit. Then the circuits that put the data on the bus count the number of bits in the word and if it is an even number of bits usually adds a parity bit so the word contains an odd number of bits. This is called "odd parity". Even parity can be used, the the usual convention is odd. Then once the data arrives, it's checked. If you picked up or lost a bit, the system flags an error.
Yes, there's an obvious flaw in the system. What if you pickup or lose two bits? Parity checking will not be able to detect that. A more complex ( read expensive) system can correct a single bit error and detect a 2 bit error.
You have this system for the PCI bus, but not the PCIe bus. Remember, PCI Express is basically a serial bus
Google "parity error" or "parity checking".