All projects lost after message in "View all", about autosave not working

Describe the bug

Arising from support ticket https://support.microbit.org/helpdesk/tickets/100034 (private)

Paraphrasing reports from a student and a teacher...

Student lost all projects saved online, after clicking Continue (the only option) on a message about autosave not working, which appeared after choosing "View all".

For about three weeks, student and teacher had worked on over 20 projects. Student was signed in, and everything had been autosaving OK.

After completing crashy-bird, the student wanted to do the "extend project" option, and the teacher wanted to show how to get to the "all programs" list, to duplicate the project.

After clicking "View all", there was a warning about autosave not working. The only option was to click Continue.

After clicking Continue, all projects disappeared, and the student was signed out. After signing back in, there were still no projects.

Expected behavior

Projects are not lost.

micro:bit version (please complete the following information):

not hardware related

Desktop (please complete the following information):

• OS: [e.g. iOS] Chrome OS
• Browser [e.g. chrome, safari] Chrome
• Version [e.g. 22]