If you've deleted all the channels and re-scanned MP loses the association between the channel IDs and the recordings (so they don't show up in MP), and deletes all of the recording schedules.
The way I fixed it was to temporarily rename the TV recording folder (so MP can't see it), then go TV server config -> recording settings -> database import, hit the 'Remove no longer existing files' to remove all the old, invalid database entries. Close TV server config, rename the TV recording folder back to the original name, then go TV server config -> recording settings -> database import (which should now have all of the recordings listed), hit the 'Import selected files' to add them back into the database.