What causes a corrupted profile

This is another potential fix:

Fix User Profile Service Failed the Sign-in Error in Windows 10

Try3 said:

The only factor I ever saw suggested was that the computers concerned had been repeatedly turned off without going through the proper close-down procedure [i.e. closing the NTUSER.DAT file].

Agree. The only time I had this Temp Profile appear was when my laptop's battery died suddenly before it could safely shut down. Combined with the HDD set for 'Better Performance' and write caching, I considered these two the major contributing factors.

I upped the Critical Level % and turned off 'Write Caching' and thankfully have not seen one since.

And as you say, wisdom received by experience.

W10 Tweaker - the first fix you mentioned is the one I have used.

Curiously, now that I think of it, all my cases have been laptops.

In all cases I have set the sleep setting to "never".

None of them tinker with Registry cleaning.

I have had customers who routinely shut down their towers with the power button (until told not to! ) but have never had the "temp" profile problem.