Hello tingyulou,
just from the names I would say:
"AutoScale once now" just scales when you say so, but when (after scaling) new data is supplied, the scaling may be wrong/bad. When you select "AutoScale" instead then whenever new data is supplied the graph scales again to fit the data.
But that's just a suggestion, I didn't test it...
Best regards,
GerdW
Best regards,
GerdW

using LV2016/2019/2021 on Win10/11+cRIO, TestStand2016/2019