I have searched a lot but couldn't find this issue.
Phone : Moto G5 Plus
Android Version 7.0 (default display size)
Launcher :Nova launcher default setting.
I have created a widget containing 5 rectangle each same size in stack group(horizontal center) .
Width = $si(rwidth)/5$
Result widget left space at left side.
If i change display size(from android setting) widget looks fine.
What do you mean with "if i change display size from android settings" widget looks fine?
Pure android comes with option to change display size. Check screenshot.
With default display size here is result.
With small display size