I think this may have been a bad interaction with a manually configured Alfred settings path pointing to a Dropbox folder and the recent Dropbox migration of local file storage to a "secure" path:
https://help.dropbox.com/installs/macos-support-for-expected-changes
I toggled the Alfred settings path, selecting the new Dropbox folder path, then restarted laptop, and now command-space is properly triggering Alfred. Resolved!