Have you received it since then?

Nope. And I just noticed that the same user pinged me again on the 7th; I did not see that either. I do not see either of these pings in the alerts drop-down atm. This has happened with at least one other user, IIRC.

Thanks.

That user's signatures look weird, it doesn't have a link to their user page (and in one case, the timestamp is off by a minute). It may be that it's not being recognized as a signature, or that the user is doing something strange like manually creating a look-alike signature. Mention notifications (annoyingly) are not sent if the user doesn't sign, to avoid sending mentions for things that aren't discussion comments.

Aha! It looks like you get these kinds of signatures if you turn on fancy signatures (the "Treat as wikitext" option in preferences) but don't actually provide a custom signature (the "New signature" field). It looks like there's probably a bug in DiscussionParser that doesn't recognize this as a signature.

I see :) So basically the parser fails if the signature does not contain a user page link? That does kinda make sense. Thanks, Catrope.

In T169852#3426565, @Cpt.a.haddock wrote:

I see :) So basically the parser fails if the signature does not contain a user page link? That does kinda make sense. Thanks, Catrope.

Yeah that's right. There's nothing in the signature that makes it particularly recognizable as a signature (to software, at least). I fear this might not be an easy bug to fix, short of fixing how mentions are done generally (see T128535: Consider ping parser function instead of link-based mention, which proposes making mentions use explicit syntax so that we don't have to guess whether you're leaving a discussion comment with a mention or adding a link to a user page while editing a non-discussion page).

While that is true, perhaps not allowing custom signatures without a user link, or as in this case, without anything at all, might be another approach to fix this particular edge case.

In T169852#3427666, @Cpt.a.haddock wrote:

While that is true, perhaps not allowing custom signatures without a user link, or as in this case, without anything at all, might be another approach to fix this particular edge case.

Yeah. At the very least, the case of "custom signature is enabled but nothing is specified" is pretty weird and should fall back to something more reasonable.