I tried to reproduce what you're seeing, Julius, and did see some pretty weird / inconsistent / not-reproducible behavior as far as viewing a window legend with and without fills. I have no active projects, so just opened an old one using the AC 17 library and let it be converted but not migrated.
In my case, whatever my view was defined as is what showed up on my layout. I was not able to get what you show. Is every setting for your view defined (no 'missing' or 'custom'?), and you are sure that that exact view is the placed drawing (perhaps drag the view again to a fresh sheet to test)?
The strange behavior I'm seeing with the AC 17 library parts sometimes responding to a Model View Option and sometimes responding to a Graphic Override (and sometimes to neither) is likely some weird thing with the old library and migration. Since your example is using an AC20 door (Ovi 20), that cannot be the cause of your view vs drawing appearance... which is why I wonder about the view settings themselves... and if the placed view (drawing) in your migrated template might have something wrong and you have to place a fresh copy of the view to resolve?
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AC 27 USA and earlier • macOS Ventura 13.6.9, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB