I’m sorry but I think it’s you. I see some issues in your SketchUp model such as incorrect tag (layer) use. All edges and faces should be untagged. I corrected that and got the following. It means there was a lot of geometry that had been tagged. Only objects (groups and components) should get tags.
It’s also a good idea to purge unused stuff from your models once in awhile.
As for the slight changes you refer to, what sort of changes are you seeing?
In LO you have moved the camera for the viewport on page 2 which can cause you issues when you are making changes to the SketchUp file and updating the reference in LayOut. As I mentioned before, it’s better to leave the camera alone in LO and just move the edges of the viewport if needed. You can see the model shift slightly when I reset the camera change you made in LayOut.
Some label leaders are anchored to points in the model and those leaders update when the model shifts on the page. The ones that aren’t anchored stay. Most of the labels for this viewport are anchored to the model. Some of them on Page 1 are anchored but many aren’t.
That’s a decent way to work although I might consider using a viewport of the actual model as a temporary reference on page 3 and insert the image from PSD directly into LayOut. It can be sized to match the model and then the model viewport deleted. (Or left on a layer that you normally hide for that page. That would make it easier to use it later if you need to.
The main problem would be file bloat. The LayOut file ends up being much larger than it needs to be because there are multiple copies of the SketchUp file contained in it. The other problem would be if some viewports are referencing one of those files and the other viewports are referencing the other file things won’t match up.
As I look at your SketchUp model more I see that you could be working in a much more efficient manner if you would use the same model throughout instead of stringing out copies of it. With appropriate use of tags to control the visibility of the various objects in the model you should be able to show everything you want in each viewport with no problem. In fact, if you were using tags correctly and since you are using SU/LO2021, you could manage to use a single scene for both viewports on pages 1 and 2. Not only would this make model management easier, it would reduce file size even more (purging unused stuff reduced the file size by over 16%).