I have an #announcements category on which every user is set to watch the first post by default.
This has been used over the years as an excellent way to send emails out to everyone.
I create a new topic in a hidden #quarantine category and schedule it to publish the topic in to #announcements on a set time and date, which then triggers tens of thousands of emails to go out.
I created a topic in the default #staff category (not the usual #quarantine category) last week without realising, and set this to auto-publish to #announcements today, which it did, but no emails were sent out.
Thinking this might be something to do with the magical built in #staff category permissions I moved the topic to #quarantine and set it to publish again, which it did, but still no emails went out.
What might cause this? 
I updated to 3.4.0.beta4-dev (5bc7371192) yesterday, which included the PostgreSQL 15 update migration too.
Is the migration to v15 likely to have caused an issue?
Is the fact the topic was created in the #staff category likey to have caused an issue?
Are there any conditions which might cause the first post of topic in a watched category to not send an email out?