OK, I’ve now got a hunch as to what it may be for, as this is the only incomplete journey in my history, although I’m a little dubious as this was back in June which I’d have thought is far too long ago:
- Stratford International [HS1] to [No touch-out] £2.80
- [No touch-in] to Elephant & Castle [London Underground] £3.85
(Total cost = £6.65)
£6.65 – £5.00 = £1.65, the off-peak Z1-2 Railcard TfL-LU fare.
(Incidentally I filtered my history for journeys costing >=£5.00 as part of the search and I haven’t taken any since Jan 2020!).