Yep, exactly the same here. It's improved over the last couple of days but I'm still not receiving all subscription alerts.
I've been using this ucp.php?i=main&mode=subscribed to check which of my subscribed threads has been updated which at least provides some sort of workaround, without having to remember thread names and dig them out.
I run my own email system and have an external company forward WP mails to me. I've asked if their system is filtering out WP mail as spam (I have little control over exactly what it is they trap as spam) but not yet received a response.
Checking headers in the update alerts that do arrive show nothing unusual by route or timing - although I have had delays of over five hours before alerts arrive here: in those cases the delays were caused by systems between WP and me.
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Giraffe: a ruminant with a view.