Just updated from 17 to 18.0.4. The custom background image that we have displays correctly on the log in page, but when loading a password protected file share page the background image is tiled.
Would it be possible to provide a screenshot how it looks like?
Did you find a way to get this fixed? I have the same issue.
I issued the same problem with shared links…
Hope there will be soon a workaround or a bugfix available.
I use random images with the app Splash. There i get no image with passwiod-shares. Not nice but ok.