Xubuntu 20.04 on Win 10: Guest additions messed up my settings

[Hiro Protagonist]

I've just installed Xubuntu 20.04 on a Win 10 Pro host using VBox 6.1.8. The installation went smoothly: I specified "log in automatically" and a password on the "Who are you?" installer page, and did a post-install software update (which required my password). However, I then installed the Guest Additions, (using sudo, which also required my password), took a snapshot, and rebooted. I was then confronted with a login screen which refused to accept my password -- it just went back to the login screen every time. I'm attaching before-and-after screenshots.

I went back to my snapshot, did a full shutdown, and then restarted. This got me back in, but there is a screensaver now (which fortunately accepts my password, so I could get in to disable it!) and the terminal window has gone peculiar.

First, it has lost my color settings (and doesn't save them after I change them, so I have to do it every time); second, if I close it and reopen it, it always gives me the "to run a command as administrator" message, as if I hadn't run sudo previously (which I did when I installed the GAs) and despite the presence of .sudo_as_admin_successful in my home directory; third, it has no command history from previous sessions.

And fourth, the strangest thing of all is an error that appears before the initial prompt: "bash: /home/me/.bashrc: Permission denied". Now, .bashrc has rw-r--r-- permissions (and I sanity-checked with my pre-GA snapshot, and the permissions were the same), so I assume something is trying to execute it directly as the terminal starts up. I have to run ". .bashrc" as the first command each time.

I have no idea what other things might have been changed!

Does anyone have any idea what has happened here?

[Hiro Protagonist]

Oh, and I just noticed that although I can resize the screen, copy & paste and drag &drop, a shared folder I defined is not being mounted. Yes, I rebooted. I'm also not a member of the vboxsf group. Adding myself has no effect, so I assume that the vboxsf group does not exist.

[Hiro Protagonist]

Hmm, I think I've solved my own problem; restarting had no effect, but doing a complete shutdown and then restarting did. Go figure.