Stat Unit Frame time larger than any unit

Hi

When stat unit, I knew that the slowest unit will be critical for a frame time,
But what is the reason when frame time is way larger than any unit time?

344543-screenshot-2021-07-20-113003.png

What particular console command did you use to get this?

“stat unit”
Please ignore the lower show messages, what I asked is the stat unit result,
Since Game, Draw, GPU, RHIT unit time are all lower than 15ms, why is frame time is 20.31ms?

Is this any use?

https://answers.unrealengine.com/questions/468611/stat-unit-frame-time-larger-than-game-draw-and-gpu.html

Thanks, I will accept the VR rendering window miss penalty as the answer.