Hi,
This is about an issue with regards to using the Slip Tool on a clip whereby Scale to Fill is used on a clip that is smaller than the sequence dimensions. In this scenario, a 1920x1080 clip is Scaled to Frame Size of a 3840x2160.
Normally, if you use the Slip Tool on any clip, it will show the in and out points of the video. However, if the clip is Scaled to Frame Size first, Premiere Pro will bug out and scale the preview shots as well, making the Slip Tool more of a guess. It should instead show the In and Out points of the video in preview without the scaling.
I thought it was just my PC issue at first but it seems like its been an issue for a number of years now. Hoping the devs can help out. I am aware that Fit to Frame Size doesn't have this issue however.