Yeah I had the same thing three days ago, but forgot to bring this up here:
A while ago, I replaced a certificate with a different one (forgot one name initially, then added it later) and I only received one expiry email which was for the ~1 day remainder, stating:
[...] Your certificate (or certificates) for the names listed below will expire in 0 days (on 12 Sep 21 17:03 +0000). [...]
[Email date header stated email was send on Sun, 12 Sep 2021 08:03:02 +0000, received about two seconds later]
The email for twenty days and ten days was never received on my end. I double checked all logs, all mailservers were fully operational and no related email was blocked.
We had also another report recently, suggesting that they had similar behaviour.
It does look like something weird is going on with the expiry mailer.