It happened on a train.
Class 365 Cambridge/London, and we were clearly (to me) not achieving the performance we should have been. After a couple of stations the driver announces that the train can only achieve 50mph and he thinks restarting it will help, and this will take a few minutes.
Everything went quiet, then started up again, the display panel ran a lot of self-tests, and about 5 minutes later we started off. This time we achieved the usual performance of up to 100mph (depending on the track) and so were only slightly delayed instead of very delayed.
I'm not sure rebooting the train is in the normal drivers' repertoire of fixes, and in any case I wished to compliment the driver on his efforts, but he was deep in conversation on his phone with what sounded like train-maintrol, so I left him to it.