Missing miles - but added instantly after completing form.

I've not seen this before, but I noticed my recent Upper Class flight did not credit miles or tier points to my account. Only the "online checking" displayed in the statement summary.
I filled out a missing miles form and instantly received the message:
"Success! Your claim for missing miles has successfully been credited to your Flying Club account. Click here to view your updated account statement."
Does anyone know why the miles didn't credit automatically? This was a London Gatwick to Las Vegas flight and my flying club number was added to the booking and showed on the boarding card.
I filled out a missing miles form and instantly received the message:
"Success! Your claim for missing miles has successfully been credited to your Flying Club account. Click here to view your updated account statement."
Does anyone know why the miles didn't credit automatically? This was a London Gatwick to Las Vegas flight and my flying club number was added to the booking and showed on the boarding card.