It is also a timing issue - between about 1am-10am EST, extensions are not available yet for the latest Slicer Preview Release (see some more information and solution here).
You need to do this only once. All recent (not more than a few months old) Slicer Preview Releases can work from the same DICOM database. If you open the same database with an older Slicer version (e.g., 4.10) then it will downgrade the database. I would suggest not to mix Slicer-4.10 and 4.11 and just use recent Slicer-4.11 releases now.