I have a registered Oyster card with Senior Railcard loaded, so within zones
1-6, my off-peak daily travel should be capped at £5.00. An off-peak day
return from Upminster to Ockendon with railcard discount, which I could
presumably have bought at Fenchurch Street, costs £2.70 - I can't see
anything indicating that minimum fares or time restrictions would prevent
the use of such a ticket at the weekend.

On a recent Saturday, I made four journeys using Oyster PAYG. The first two
may have been linked by an OSI. I don't think I had any time-out issues. I
started the day with a balance of £14.06 and ended it with £4.66, so I was
charged a total of £9.40. Paper tickets would have cost £5.00 + £2.70, a
total of £7.70. Why was I charged £1.70 more? Is it anything to do with
the anytime day return (undiscounted) from Upminster to Ockendon being
£4.40?

Details, which I don't fully understand (even individually):
Victoria - Tower Hill: In £4.20, out -£2.40, so charge was £1.80.
Fenchurch Street - Ockendon: In £2.40, out -£0.45, so charge was £1.95.
Ockendon - Fenchurch Street: In £5.60, out -£1.70, so charge was £3.90.
Fenchurch Street - Liverpool Street on foot!
Liverpool Street - King's Cross St. Pancras: In £4.20, out -£2.45, so charge
was £1.75.