@rhessinger Thank you Rich - will install it once released and confirm it is fixed.

To follow up, we ended up being able to get everything working using userPrincipalName for user identity by switching to the OpenLDAP/GenericLDAP connector. The remaining issue I was seeing - unexpected failed group lookup in the "Test User Directories/Load user by user name" test - appears to have been caused by a quirk in the connector. In this particular test for this particular connector, group names are case sensitive. In the other tests for this connector, and in all the tests in the AD connector, group name case is ignored. This does not seem to have any repercussions in actual use, but it led us a merry dance for a while.

Thanks for the comprehensive response - which was very helpful. Closing the loop, we've elected for the short term to run up a parallel aptly server to manage our existing apt snapshots, but in the longer term we'll revisit how we use snapshots at all and very likely will switch our process to use upstream provided snapshots.