journal contains errors on each service restart "keyword is not comprised only of uppercase ASCII letters or digits"

Some systems have been reported to emit errors to the log on each libvirtd restart.
An example is:

libvirtd[15231]: internal error: The keyword is not comprised only of uppercase ASCII letters or digits
libvirtd[15231]: internal error: A field data length violates the resource length boundary.
...

Such messages can almost always safely be ignored.
It almost always points to device/firmware reporting invalid VPD data.

Libvirt is ok to stumble over this, but maybe reporting it as an error is too much.

Note:
If you are affected and you wonder which device is causing this you might run the following:

$ for i in $(sudo find /sys -name '*vpd' | awk -F '/' '{gsub(":","_"); gsub("\\.","_"); print $6}'); do virsh nodedev-dumpxml pci_${i} | grep -q "capability type='vpd'" || echo "device ${i} has invalid VPD data"; done
device 0000_02_00_2 has invalid VPD data
device 0000_02_00_0 has invalid VPD data
device 0000_02_00_3 has invalid VPD data
device 0000_02_00_1 has invalid VPD data

So in my case I've found 4 entries being broken, and when looking into those they are 4 functions of the same device which is the one with the bad firmware.

If you can check if updating the firmware fixes the issue for good.