I'm having trouble with the first core 21 (WU 9704) that I'm aware of, TPF of 2 hours and a 5 day ETA using a 980ti.

Running one Core 21 on my AMD today, so far so good. http://weather.mfc-cs.com/haf/Foldit-2-AMD-R9-290X%20Slot%2001.html
 

I have been getting a lot of core 21 WUs of late and have had no problem folding them.

That's on par with what mine 2 x 980s run at.

I had low PPD issues with x21 I did not noticed any failed ones tho.
 
I would honestly delete all the FAH files ( complete uninstall, app data ,ect) reinstall, replace the gpu.txt file with the once from the website and make sure your NVidia power settings are set to maximum.
 
All my folding clients craped out this week, full reinstall fixed it. my 350k+ ppd dropped to 70k.
Running client-type beta forced only core 18 on my 970.

These Core x21 projects are cooking my video boards. I Folded all day yesterday and my video boards currently on a custom watercooling loop never went over 48°C all day long folding Core x18 projects. After taking a break for a few hours I started to Fold again and snagged a Core x21 that made my board temps shoot up to 55°C. Just like the night before when I got a Core x21, I had to take the side panel off of my case and have a floor fan blow extra air into the case and through the radiators to get the temps back down around 49°C.
 

 

146Kilos
Your kidding, I thought sub 90C was acceptable ?
If 55C is "cooking" my 980 would have been toast months ago, it runs in the mid seventies all day (or would do if I folded all day).

LOL, mine was in the mid to upper seventies on air too but the watercooling brought the temps down considerably. I'm still in the learning phase of watercooling my video boards but a sudden 7° jump is rather noticeable even to a novice like me.

I can get the temps down a fair bit due to a nice cool (UK) climate but at the expense of some noise, my fan profile ramps up steeply from 75C upwards.
Talking of noise, has anybody else had those tiny core 21 units that take 45 mins to complete ? My card was making very strange noises working some of those, not at all coil whine, more of a growling noise, most odd.

Have not noticed it on my 980 Hydro Coppers but then again I do have some hearing loss.
Spent way to much time in combat as a Ranger in Vietnam for 18 months.

My two 980 Hydro Coppers clocked at 1500 Mhz never get above 45c even when folding two core 21 work units at the same time.
The cards are cooled with a Black Ice Nemesis 360 radiator with three fans in a push configuration, water cooling is the way to go.
My AC sure runs hard when folding with the heat we have in southern Oklahoma, just a stones throw from Texas.
In the winter my heating system runs very little, the PCs keep the house warm.
I have all the parts now to build my 2011 Intel 4930k rig with two Titan X Hydro Coppers.
Sure wish I had an able body can only work on it about 30 min at a time, then that is only with one half of my body as the strokes took out the use of the left half.
Want a challenge try building a pc with one hand arm and leg, for that matter this very long text SORRY.