First, multi-user and gnome are working for me in buster after a full upgrade from stretch. That's not the problem.
When I just boot and let the system try to boot into the default multi-user, it hangs very late in the process, right after the console message about invoking gnome. The next boot message concerns using Cntl-C to abort filesystem checking. (Cntl-C has no effect, though.) After about a minute there is a message about the sound card. And then no new messages or any change after a long wait. I can ssh into the machine and it seems to be working and this is the only clean way I can reboot it as it won't respond to anything like cntrl-alt-del at the console.
If I boot into recovery mode and simply type control-d when prompted for root's password, I boot into the gnome gui. All is well. So my problem is merely an annoyance, not a show stopper. But this shouldn't be happening. Any suggestions on how to proceed? Some grub thing? Thanks.