MIG wrote:

It may depend on the station and how it's programmed. A few months
ago, forgetting that I was on pay as you go instead of travelcard, I
avoided a blockage at Euston by being waved in through the open gate
by a member of staff and didn't think of touching.

On the train I realised that I hadn't touched in and might face the
penalty.

I got off at Bank (roughly as planned), went via the DLR platform and
touched "in" at the mysterious DLR pads, then went up the escalator
and out through the barrier at Monument, where I was charged for a
single journey in zone 1.

Where I was meant to have been I don't know.

And I assume you checked your journey history at the earliest possible
opportunity?
--
David of Broadway
New York, NY, USA