I've just had an email saying my pay as you go Oyster auto top-up failed
(on W15 bus) on Friday because it couldn't charge my credit card. But
I've just logged in and resettled using the same credit card. What
gives? It's worked fine for six or so auto top-ups before and the card
doesn't expire until next year.

The only thing I can think of is that on Friday I made a lot of atypical
journeys in the east end - could it be some anti-fraud algorithm?

E.