The usage increase lasts for 2-3 seconds and causes stuttering video playback on the second screen and overall jittery system performance.
This is on a 3900x/2070 Super/32 GB system. Drivers are up to date.
Switching to low/med/high graphics settings in Hearthstone does not seem to have any effect.
The spike coincides with increased GPU usage of the Desktop Windows Manager process.
Closing Hearthstone eliminates the spikes completely (including the DWM spikes).
Monitoring without running any other apps, just Hearthstone idling, the spikes are happening almost like clockwork.
Unfortunately, the forum won’t allow me to post images/links from the Taskmaster monitoring page.
I have posted a similar thread on r/hearthstone including the screenshots.