Inconsistent New Thread Emails

Since Saturday, I've received notifications about 13 new threads in my Watched Forums (NSFW Questing & NSFW Creative Writing), but only received emails for 6 of them. I had noticed that I had received an alert, but not an email, about [NSFW] Bespoke Fucks by Nugar; so I double-checked my thread settings to make sure I was set to received emails, then didn't get an email about [NSFW] Fires Of Industry [RWBY]; so I unfollowed and refollowed the forums, then didn't get an email about [NSFW] A C'tan in a World of Bloody Evolution.

Now, I haven't received any New Thread emails since [NSFW] Alter (R34 Economy/Warhammer 40K SI) on Monday morning, so it might currently just be broken; but over the weekend, I received alerts about 9 new threads but emails about only 5 threads.

My New Reply emails seem to be functioning normally. I've checked my spam folder. I received emails from both threads and missed emails from both threads. I don't see any connection between thread authors (for example, I neither follow nor ignore any of them) or thread content (such as images or word length).

Minor Update: Just got an email, so it's 7 emails to 14 alerts since Saturday.
+ Another alert with no email. 7/15
+ 8/16
+ 9/17
+ 9/18
+ 10/19

Major Update: seems fixed. That week was as bad as it got: it slowly improved over the next week, and for the last few days, I haven’t missed anything.

 

I've also had this issue with new post emails in the last couple of weeks. I've checked my spam folder and my follow settings.