Yes - Scene browser position: Inside.

> Is it possible that it's dependent on having a lot of different named objects and not actually file size?

My experience - If "loading file" dialog is appeared, then side panel is always expanded, no matter amount of named objects.
It seems that it isn't specific file size, probably geometry complexity determines, if "loading file" dialog is appeared and then side panel is collapsed or expanded.

Mik

Hello Michael,

I have new observations regarding this issue.

When I open same complex geometry saved as 3dm and STEP, so 3dm file is open without "loading file" dialog with collapsed side panel, STEP is opened with "loading file" dialog with expanded side panel.
DXF file is opened always with expanded side panel no matter complexity of geometry.

Mik