Is it possible that the Front Panel of the VI you are inserting is HUGE, mostly empty space, and when inserted, it shows some of the empty space?
To help us to understand and perhaps "fix" your problem, we really need to see it. The best thing to do is to attach both the VI that includes the sub-Panel (and which does the "Insert") and the VI that gets "inserted". Note that both @GerdW and I (and many others who could help you) are running older versions of LabVIEW, such as LabVIEW 2019 or 2021 (but not 2022 or 2023), so you may need to "Save for Previous Version" and attach the (say) 2021 (or 2019) version. If you are using an even earlier version, we will (probably) be able to open it.