I had a problem with receiving an e-mail for a LCY-DUB flight I booked a few weeks ago - in fact, it's never arrived, and in the end I had to enter the PNR manually in MMB to get it to show (luckily the receipt page had cached in my browser and I could go back to get it, having forgotten to note it down in my rush to leave the house).

I almost convinced myself at one point that completing the booking had been part of some bizarre dream, but it still shows in MMB now and I'm pretty sure I've been awake - if not entirely compos mentis - since then.

So, a similar experience to the OP, but just the once rather than a pattern.