I get a blank full score when importing xml from Sibelius (tried with both .mxl and .xml). The first few times I imported into Dorico this didn’t happen. But now it always happens. I tried making a very basic score in Sibelius (no dynamics or tempo or anything) and it still doesn’t import properly into Dorico. Yet the strange thing is that I can view individual instruments.
Sounds like you’ve managed to muck up your default layout options. Quit Dorico, go to /Library/your-user-name/Application Support/Steinberg/Dorico, and delete each file you can find whose name starts with layoutOptions…, then restart Dorico, and you should be OK.