Hi guys
Depending on what settings are chosen in eb when updating from 5 to 5.1 all css disappears both on the frontend and backend. By reinstating your new out of the box settings.json, css is reinstated. It took me a while to figure out that it was settings.json causing the issue, but I am not sure which setting or settings are causing the break. I fixed the issue by re-selecting from the new settings.json.
Also when nickel theme is chosen the selection of grid 1, 2, 3, 4 ect does not save and remains set on 2.