Further information:

A few minutes later, an edit with {{ping}} was made to a different page on mw.o within my user space. I got an email notification for that, but my toolbar still isn't showing any notifications.

The watchlist one is T29884: enotif doesn't send email if page on watchlist edited following a minor edit and enotif not configured to send minor edits.

Can you provide a diff for the {{ping}} edit (it should show in your Echo toolbar, unless it didn't follow all the mention requirements)?

Or rather T29884: enotif doesn't send email if page on watchlist edited following a minor edit and enotif not configured to send minor edits.

I am watching a page. Someone makes a minor edit to the page. It shows up in my watchlist, but (correctly) does not light up the toolbar, nor does it generate an email. Then the same person makes a non-minor edit to the same page. It correctly shows up in my watchlist, and incorrectly does not light up the toolbar (nor does it send email). Additional non-minor edits continue to not generate notifications.

Note: There are 2 different systems, that are NOT interconnected, but are mixed up in this description:

1. enotif - this is the ancient system, for getting emails about changes to pages you watchlist. It does not affect the toolbar, at all, ever. - The only user-configurable option is "Email me when a page or a file on my watchlist is changed" in e.g. https://www.mediawiki.org/wiki/Special:Preferences -- The main limitation, beyond the bug that Matt linked (and those linked therein), is that it will not send any further notifications until you've manually visited the page.
2. notifications (aka echo) - this is the newer system, that has various features, configured at e.g. https://www.mediawiki.org/wiki/Special:Preferences#mw-prefsection-echo - It is this, that will show a yellow "you have new messages" in your toolbar, if-and-only-if someone edits your user talkpage (but not userpage - that feature request is T3876), amongst other unrelated features.

In T164442#3233860, @Mattflaschen-WMF wrote:

Can you provide a diff for the {{ping}} edit (it should show in your Echo toolbar, unless it didn't follow all the mention requirements)?

It did not follow the requirements (diff) - requirements. -- I've sent another ping, which will have worked.

I've sent another ping, which will have worked.

I did receive that ping, both in my notification bar and via email. I have lost track of what that confirms or refutes.

In T164442#3235689, @ksmith wrote:

There is a real (non-user) page which I am watching. If it gets a minor edit, and then a non-minor edit, my notification bar at the top does not light up.

The notification bar at the top never lights up in response to a page on your watchlist being edited, that's not a feature that exists or has ever existed. What it does do is light up if your user talk page was edited (regardless of whether it's on your watchlist), or if someone comments on a Flow topic that you watch or creates a new topic on a Flow page that you watch. (Given the latter, I can see where the confusion might have come from.)

Ah. Thanks for the clarification, @Catrope . It never occurred to me that was the case. I guess even when I read claims to that effect, I wrongly assumed that my issue was being misunderstood, and not that I misunderstood how the feature works.

I really do hope that T29884 gets fixed, because the current behavior makes watching pages VERY unreliable.