@Andro yep - totally fair question.
The “suddenly” part is because %{header_instructions} isn’t something you changed locally: it’s a core-provided block that Discourse injects into a number of notification emails. If core changes its wording or when it’s included, everyone will notice immediately even if no admin settings were touched.
I don’t want to overclaim without a specific commit reference, but the most likely cause is a recent core change to the default text that %{header_instructions} expands to for watched-topic notifications (for example adding the “Someone replied to a topic you are Watching.” line), or to when that block is included in the email body.
How to confirm where it’s coming from:
- In Admin → Email → Email Settings → Templates, look at the notification templates your users receive (watched / tracked / replied / mentioned).
- If the body starts with
%{header_instructions}, that’s the source of the new prefacing text. - Removing it, or moving it below
%{message}/%{context}(or even%{reply_instructions}), will revert to the previous “plain” behaviour.
Unfortunately there isn’t currently a site-wide toggle for this. Each affected template has to be adjusted individually, which is why this feels abrupt and hard to control when core behaviour changes.
If you’re on hosted Discourse, the practical workaround is just editing the small handful of templates your users actually receive, rather than all of them.