IIS application using application pool identity loses primary token?

Question

(This is a question about a vague problem. I try to present all relevant data, in the hope that someone has helpful information; apologies for the long description.)

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Answer 1

This is also relevant for Umbraco using Active Directory authentication. From time-to-time you may get this exception:

Configuration Error

The specified directory service attribute or value does not exist

This is apparently caused by the problem outlined here. A reboot invariably fixes it.