How to get rid of Lumen indirect lighting flickering?

Yesterday I tested rendering animation with sequence.But I found the indirect ligthing side has flickering.I think my setting is very high but the problem is still there.
Later, I switch PPV, the Global illumination - from Lumen to Screen space,the rendering is much better.I wonder how can I get very clean rendering?Or this is Lumen bugs?
Anybody can help?Thx!