have a totally different motherboard but same problem, found this thread via google
bluetooth working fine, computer was asleep for 3 hours or so, woke it up and bluetooth is gone. i've updated motherboard bios, disabled/enabled XCHI, done many things... but nothing will sync any more. just to confirm it wasn't my keyboard at fault, i tried syncing it to my legit macbook pro and it pairs without an issue.
booting into windows on the same machine and i experience the same - can no longer sync bluetooth even though it was previously working fine
i too agree that it's hardware. this issue seems far too common though, which is pretty strange.