I also have this same motherboard, and had this Eithernet/USB keyboard issue for about a year now, but since I usually left my PC on, it didn't manifest. Recently to save energy, I started to use WOL from Sleep, and when the system came back from Sleep, I started having the same issues of the keyboard not being recognized, and the network adapter disappearing, along with the disks that were plugged into the Intel SATA ports would not show up. I had been powering off/on and resetting the BIOS to defaults to get rid of the problem when it happened like most here. One particular thing I noticed was that sometimes when I held the blue CMOS clear button on the back, it would boot back up with the same problem, but mentioning that the CMOS checksum/settings were corrupt...
Yesterday I looked for this problem online and stumbled upon this thread. I saw the post about changing the CR2032 battery, and just gave it a shot now. So far it seems to have eliminated the problem. I decided to do the fix given the corrupt CMOS message I was getting at times would match up perfectly with a failing battery. I will test a few more sleep/wake up cycles just to make sure that the problem is indeed fixed with this.
Thanks to all who contributed!
Edit: Tested four consecutive sleep/wakeup cycles, and no issues. Before the battery change, the problem would occur maybe 1 out of 4 or even 4 out of 4 times. I am calling this one solved.
Also, shame indeed on Gigabyte for going with a cheap CR2032, haha.