Hey @zutrinken, thanks for the screenshots! I can see why this is surprising when you’re using an empty frame to reserve a slot.
Could you check whether the parent frame is using Latest in Auto layout settings? This looks like the recent auto-layout update that brings sizing closer to CSS flexbox. With the updated layout, children set to Fill container share equal content widths. Padding adds to each child’s overall width, so an unpadded placeholder can end up narrower than its padded siblings.
Giving the placeholder the same horizontal padding (and matching any inside strokes) should keep all three the same overall width. If you want equal-width slots regardless of their padding, you can also use grid auto layout with three equal 1fr columns. If you want a bit more info on these changes in general, see our help article on using auto-layout with CSS flexbox in mind.
