Optix Render not constantly full use my CUDA And make render crash or not working

I had run into this situation several times in the last few months, the viewport rendering often cancel especially when I use two GPU render. and I have to reboot my PC to try it again.
And yesterday, while I am rendering, I notice it stop rendering after a while. and the only message I got from the console is “TIFFFetchNormalTag: Warning, Incompatible type for “RichTIFFIPTC”; tag ignored.”
which should not be the problem I suppose.
So I check the task manager to see why it’s not rendering without any error.
What I found interesting is Cuda Usage.
If the viewport or rendering works fine, the Cuda usage will always constantly maintain at a high rate at around 90%.
but when the viewport render or the real rendering works very slow or even just cancel. I notice the Cuda usage graph like sin(x), here is the screenshot
this happened to both GPU.
I have no idea where should I post this for help.
Any suggestion on how to solve this or anywhere should I post this to get some help?

If i only use one GPU, It seems works fine, the Cuda usage constantly maintains a high rate.