We have a Community that runs on a custom domain with a visualforce homepage. Now the homepage does not open anymore.

Without an account: ERR_TOO_MANY_REDIRECTS
With an account you get a Visualforce error page: "there has been an error during loading a visualforce page."

In the org there was an update on Volunteer management and UI Lightning flow was enabled.

What could be the cause here?

If your trying to run the latest DataLoader 49.0.0 on a Mac with OS 11 (Big Sur) beta it'll only show you blank windows.
This happens also with other Java Apps using older versions of the Eclipse SWT libraries (and is a known issue).
Can we expect a newer version of Data Loader using the latest Eclipsw SWT libraries in the package?

Thx - Andreas