You are not the only one 9.8 it seems does have an issue trying to squeeze additional hashes from the GPU it seems the miner does loop out certain instruction resulting in a dropped hashrate.
The other i would do is run a resource monitor with logs to make sure that you don't have any Malware/miner/something thats hogging resources when it detects idle (just to be safe try a clean install if its not too much) there are resource hogs out there that will mine when your PC is idle in background and you may have gotten infected.
Lets us know about your progress...
Will do, that Def could be the source as it is only when it detects idle. I tried a little sneak around by installing a mouse jiggler last night I will let you know if that works.