Okay this was an issue caused by “auto mute” which is triggered if you use the link through the browser URL bar, but not seen if you create a link on the page the video is on.
I appreciate “auto mute” is a browser feature.
Okay so took the gamble and bought the PRO version and now can answer my own question…
Playing YouTube and Vimeo as playlist requires pro otherwise the player will use the YouTube and Vimeo embedded players which will only play the first video in the playlist.