Hello,
I don’t remember this behavior from Beta1 but I might be wrong, anyway in Beta2 when switching from Source to Preview in “View > Document Display” there is annoying short white flash of the entire document area before the display changes. This is probably only noticeable in Dark Mode.
BTW I know you don’t recommend this but FWIW have switched to DT3 since Beta1 on my production machine (after making a backup of everything of course) and the experience has been as smooth as butter, including WebDAV sync to iOS. Not once did I have to go back to DT2.