Invisalign: My lower tray is not all the way down on my back teeth. Is this normal?

I am on tray 8 now but I am able to take my lower tray off just by using my tongue and popping it off. The reason why it is so easy to take it off is because it does not go all the way down on my lower back left side of my teeth. Should I go talk to my orthodontist about this or is it normal? My top tray fits perfect it's just my lower tray doesn't go all the way down on my teeth anymore.