Yes, this is one of the most likely reasons.
Keeping a connection attached to the player properties/events can also cause this.
References to players in a case like this should be reported in the ‘Unique References’ tab. If not, such a big chunk of memory should be easy to find in the ‘Graph’.
Consider testing out the new Player and Character auto-destroy behavior: New Player and Character Destroy Behavior
Or try to clean up the references manually if that doesn’t help (maybe you have a table where all players are recorded forever).