more than six months ago, I created a post here and answer (as well as the real reason) I have not found. https://answers.unrealengine.com/questions/420358/lag-pc-on-ue-content.html
A few months problems with UE I did not have, and I did not betray value to why. But, today, putting sound card (which I handed over to replace) in PC again and setting it software I have started again lags in UE.
Lags appear when running the sound card software. To get rid of them, need to turn off the sound card software and restart the engine.
My sound card ASUS Strix SOAR
Driver version tested all and all is lags.