There is apparently a problem with Oystercard capping at the moment. I
have had my card swapped but it is still happening. According to the
Oystercard helpline, if you top your card up in the middle of the day,
it is resetting the capping, leading to charging being restarted. They
are aware of this and are attempting to fix it. Anyone using PAYG
would be well advised to check their journey history.