Maybe Alexa has trouble understanding the word "Elbow?"
As a test, try changing the name of your playlist to something more unique sounding.
I had a similar problem with Alexa understanding certain words. For my home automation setup, I created a group that controls all of my home automation devices. I named the group "house" and I also tried "entire house." For some reason, Alexa is unable to find the group, even though I clearly say, "Alexa, turn off the house [or entire house]." I've since changed the group name to "all lights" and Alexa still has some trouble understanding, but it does get it about 50% of the time.