I've had a few events on the Big Island - one train back from Holyhead, about 2005, had the in-car automated station announcements one station out all the way back.
On another occasion, 1998ish, we ended up down some virtually disused siding somewhere around Queensferry, and had to reverse back out onto the main line.
In 1999, I took an interminable diversion, on the way from Bristol to Birmingham, as they weren't confident that the thing we were on was running well enough to get up the Lickey Incline.
I woke up once to hear a very gentle clickety-clack, when our intended route was all continuously-welded. We were doing about 20mph as we trundled along to get back to a 'real' track. That was about 2000.
I found a quiet carriage and settled down on a through train to Holyhead, about 2007. Luckily, when it stopped at Chester, the front was well off the platform end and the driver found me on his way back to alight onto the platform - and informed me that my bit of the train was being detached from the continuing part - first I'd heard of it.
In 1963, waiting with my father at Kingham, it became clear that his train wasn't stopping, and we all went off to the next station in the station master's Morris Minor van.