That is interesting, you would think ASRock would make note of that situation in the manual.
I was thinking possibly it was related to the formatting of the floppy. Since the UEFI does not like extended partitions on a secondary internal or external hard drive during boot, maybe there is a correlation. My USB floppy seems to work fine.
All I might suggest is to disable the controller in device manager. Then reboot and re-enable it after rebooting to see if it might be picked up then. You may have to do a device search to find the controller, but since a floppy doesn't act like a USB device, it may not help. If it doesn't, boot without a floppy in the drive, if you have not already done so.