I have some more information.....
As mentioned, "Adam Hills: The Last Leg" had disappeared from My Series on the website, which is set to display All recorders. I now recall that the series was originally set for my Beyonwiz.
When I re-added the series I set it for my Skippa instead, and it appeared as expected in My Series for that device.
What I have now found is if I select Beyonwiz in My Series the original entry is there. Likewise, if I select Skippa, the new entry is there. If I select All then only the Skippa entry appears.
I can accept that the My Series "All" option can't or won't display duplicate entries for the same series on different devices.
What is a mystery is why the original Beyonwiz entry disappeared from the All list.