version 2.7
I find that often the related videos are not as closely related as they should be. I know there are other videos with the same tags but they don't show up- even in a related list of 8 videos.
For example, playing a video with tags (John Rutherford legislative assembly buds guitar store Mountainview Music) will not even suggest a video that has tags (John Rutherford East Coulee Spring Fest buds guitar store) because only the 1st two words and the last 3 words are the same.
Changing the order of the tag words does not fix the problem.
Is it using the username to sort? The same user uploaded both videos.
Is it grouping suggested videos by the video_seo_name in the database? For this example the artist name and the song name were switched in the two videos.
It suggests lots of other videos because of other words in the tags. Very odd.

You can try this out on the site Casselmans Canada - Canadian Arts & Entertainment
Try these two videos. You would think they would recommend each other.

Casselmans Canada - Bud's Guitar Store - John Rutherford
Casselmans Canada - John Rutherford - Bud's Guitar Store