If notformat=text is passed to ApiEchoNotifications, it deletes all notifications instead of returning any of them. It does not seem that this is reversible without directly editing the database.
It looks like rECHOcf7100963849: Remove deprecated formatter removed the "legacy" formatter that notformat=text was attempting to use, causing formatting to just fail, and rECHO6e2236db8109: Moderate notifications caused Echo to delete notifications that cannot be formatted.
The best thing may be to just remove the 'text' option if it's no longer supported.