Why do Pinned Start Menu items periodically disappear?

Every few months, all my pinned Start Menu items in my Windows 10 setup disappear, and are replaced with a "Productivity" group. I mean this literally: every 2-3 months, over a period of maybe 5 years.

It is sending me up the wall.

For info, none of the stock cut-and-paste textbook responses typically seen on the Microsoft Forums will serve any purpose here:

1. The resource checker found no "integrity violations"
2. The deployment tool said the operation completed successfully, but didn't tell me what the operation was. The machine wasn't "deployed"; it was hand installed from media, so I don't know if I'd expect it to yield anything useful.
3. The directory %LocalAppData%\Packages\Microsoft.Windows.StartMenuExperienceHost_cw5n1h2txyewy\LocalState does not contain the expected start.bin file.
4. The directory %AppData%\Microsoft\Internet Explorer\Quick Launch\User Pinned does not contain the expected StartMenu folder.

I've used variations of Windows over the last 35 years from around Windows 3.1, and I know a few tricks myself, but this one has me baffled.

• What could create the Productivity folder?
• Why are my start menu pinned items not stored at the normal place?
• Is there something in the registry which is causing them to be stored elsewhere?

Anyone who might have an idea, your help would be greatly appreciated.