Helen Deborah Vecht wrote:
Reviewing my journey history from a recent weekend day trip, I see my
Oyster was charged £1.50 one way from Z4-Z1 and £1.00 the other. There
were no other journeys on it that day, so capping didn't apply.

I think the fare should be £2 each way but if the card has been used
correctly I can't be held to be cheating. As the journeys were made by
my partner, there is little chance of identifying which gates were
involved.

You're correct - the weekend fare is £2 each way for that journey!

Has there been a recent systemic glitch which could deprive TfL of far
more than my trivial £1.50?

If if would help ease any guilt you may have, I've been overcharged by
£1.50 in the past but felt it's not worth the hassle to phone them up so
not bothered :-)