I tried both and same thing. Weird thing is it’s only happening on certain files. Not very large. By when I don’t restart my computer and leave the lagging alone, I can open other files and it doesn’t happen, and then when I reopen certain files, it lags. After I’ve changed the font to Arial and while the internet is off.
How many edges and faces in your model? (Model Info>Statistics, check the Show nested components box)
Is there a way to “reset” things? Un/reinstall SKUP?
That might work on Windows, on Mac the best approach is to delete the folder and removing the app icons from the dock, empty the bin, restart the computer and than install again by ‘mounting’ the disc image (.dmg file) by double clicking on it, and then dragging the SketchUp icon into that of the applications icon in the panel that appears.
I had similar on an imac 2012 i7 16gb 1536mb graphics. I just assumed it was the computer struggling.