Now that we have Herald failure logging thanks to T370266: Update to Phorge upstream 2024.35 release, we see that H455 fails:

PHLOG: 'An exception occurred executing Herald rule H455: "Array for %Ls conversion is empty. Query: project.phid IN (%Ls)" Review the Herald transcripts and correct or disable the problematic rule.' at [/phabricator/src/applications/herald/engine/HeraldEngine.php:540]

because its condition Project tags incl their milestones (use with None only) is used with include any of. Which is not None. :)
Background: rPHAB86034a82 is a hack for T144041.

Any idea how to make it clearer to only use with include none of?
Should we rephrase to Project tags incl their milestones (only use with Include None Of)?

Heads-up to @greg as its author (who's aware of this anyway due to T383187).

As this was failing anyway, I tried changing the condition in H455 to Project tags include any of. But that doesn't work either.
Sorry, Herald support for subprojects is... meh.

So either we disable the Herald rule. Or we manually add each subproject to the condition.