Two friends have a serendipitous encounter with a Caribbean musician, in a London park, only to discover the bitter sweet truth about life through the recollective storytelling lyricism of their new found friend.

I could be cynical and say "to discover the bitter sweet truth about life", I only need to get up in the morning. I don't need to go to the movies.

The big problem here is that "the recollective storytelling lyricism" screams: talking heads!
This logline is not promising a movie. It's a novel or at best: a play.

If the musician tells more than one story, pick one and SHOW us this one. And better stick to one protagonist because right now it sounds as if there are three, which I haven't seen done successfully by anyone lately.

Any great screen story is about a character wanting something and having difficulty getting it. I'm not seeing any of this in the logline.

Perhaps have a read of the tips elsewhere on this site and it may help you what exactly to include in your logline.

Happy loglining!