Unable to download subtitles

[MagratG]

YouTube-dl failed to download the subtitles for this program that it had found.
I've managed to download subs for other programmes that had them.

V:\YouTube-dl>youtube-dl --all-subs --skip-download https://www.itv.com/hub/agatha-christies-marple/9Da13066
[ITV] 9Da13066: Downloading webpage
[ITV] 9Da13066: Downloading XML
WARNING: Unable to download XML: HTTP Error 504: Gateway Time-out
[ITV] 9Da13066: Downloading JSON metadata
[ITV] 9Da13066: Downloading m3u8 information
[info] Writing video subtitles to: The Body in the Library-9Da13066.en.vtt
WARNING: Unable to download subtitle for "en": Unable to download webpage: HTTP Error 404: Not Found (caused by HTTPError()); please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; type youtube-dl -U to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.

V:\YouTube-dl>youtube-dl -v
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: ['-v']
[debug] Encodings: locale cp1252, fs mbcs, out cp850, pref cp1252
[debug] youtube-dl version 2020.06.16.1
[debug] Python version 3.4.4 (CPython) - Windows-10-10.0.18362
[debug] exe versions: ffmpeg git-2020-03-15-c467328, ffprobe git-2020-03-15-c467328
[debug] Proxy map: {}
Usage: youtube-dl [OPTIONS] URL [URL...]