I’ve had the same issue appear in Windows 10 64-bit on one PC but not on the other.
I’ve been a paid user of Avast Pro for some time and sure enough, a test uninstall resolved all my DPC latency problems.
Interesting that after so much time, this issue still occurs and a pity too because up until now, I had been very happy with Avast.
Will test again with only Antivirus installed and report if any improvement.
Thanks to the original poster for helping me resolve an issue that has been driving me nuts for weeks!