Logs from a run where you press that button and nothing happens would get you further...
The log does not say that anything in regard to Updating was done, so maybe the skin is outdated? Did you test defaultwide?
Added subtitle support to watch-series.
Do an update of the site, install https://www.team-mediaportal.com/extensions/movies-videos/subtitledownloader, in the onlinevideos config select watch-series, and fill subtitlesource with one of the subtitlesources supported by the subtitledownloader (remember: it's case-sensitive), and optionally subtitlelanguages.
I've only tested with bierdopje, so there may be some issues left.