Thanks for taking the trouble to reply. The DVD machine in my editing space is a Sony RDR-HX525. It’s used to check all DVDs I make before passing them on. This is the first time anything untoward has occurred. (See note later). I have partially solved the problem. I dug out another DVD player and the disc plays fine as required. This machine is a Sony RDR-GX700. Both of these are quite old now but were top of the range at the time. So, as you say, this disc might be incompatible to this one player.
I have now made a DVD-R disc as suggested but exactly the same problem on the one player.