There is an issue with nvidia drivers, but it seems that it doesn't happen to everyone, but just a lot of people. Reinstall windows won't help cause it happens even
in windows 7 and windows 10 so it's not a windows issue.
started to happen since 360.x drivers
364.96 Hotfix nvidia released to fix the P-state issue didn't help.
The clock after being idle just stuck on P-State P5 , clock and memory doesn't go to the max.
Only fix is Disable/Enable the Display driver OR Apply Clock (no need to overclock just +0 +0) bring the clock and memory back instant OR Restart computer.
I opened Nvidia ticket and they said it's a known issue and they are investigating.
http://forums.guru3d.com/showthread.php?p=5262578#post5262578https://forums.geforce.com/default/topic/916069/geforce-drivers/gtx970-clock-rate-throttling-and-tem...https://rog.asus.com/forum/showthread.php?84751-GPU-Tweak-2-clock-issues-(1-2-0-3)There are more threads.