I have a similar issue - Layout does not remember the Page Setup dialogue boxes at all. I have A3 landscape set as the default in Preferences, which works fine, but if I then open Page Setup, select my A3 printer and A3 paper, save and close the file, when I reopen it those settings have reverted back to the default. This can’t be the correct behaviour surely?
Update - I see that it uses the default printer settings from System Prefs - I have an A4 laser as the default. If I change that to my A3 laser, it shows the correct settings in Page Setup. That doesn’t excuse it as bad behaviour though, in my view.
SketchUp Pro 2016 - OS 10.11.6