UnEXCELlent jumplists on Windows 10

I was seeing very odd behviour with Excel (pinned to Taskbar) jumplists under Windows 10. Only Excel, of all the Office products, was showing this behaviour. .xlsx files, accessed locally, were placed into the jumplist, but without the Excel icon. Clicking on the jump list entry produced the message "The item that you selected is unavailable. It might have been moved, renamed or removed. Do you want to remove it from the list?". The file, of course, was still in place. This only happened for .xlsx files; other Excel file types on the jumplist, such as .csv and .xls files worked as expected. .xlsx files accessed via the OneDrive folder also behaved correctly.

Even more weirdly, if I moved one of these "missing" files, deleted the jumplist entry (which stayed on the jumplist), then clicked it again, the .xlsx file opened successfully in its new location. Then it would cease to work, as before.

Only my user on the machine was affected. If I logged in as Administrator, Excel jumplists worked as expected.

The web provided a number of remedies. I tried all these to no avail:

There was only one option left I could think of; creating a new user profile and migrating to that. My existing user profile was over 30GB; perhaps this had something to do with the issue. I first had to convert my existing user to a local account, then I could create a new account based on my Microsoft account login name. Excel jumplists for the new user worked.

To effect the migration to my new user, the following steps were required: