I've tried updating Extension Manager via the Joomla Updater, via the Extension Manager Component, and also manually by downloading the package. All result in 'success' messages but indicate the upgrade installed 7.4.4 again. The other Regular Labs extensions won't update until the extension manager updates to 7.4.6, so they're stuck as well.

Also, the most recent version shown in your change log is 7.4.4 - www.regularlabs.com/extensions/extensionmanager/changelog

Thanks! That worked.