Its possible that the glue did not get on the “crossing” of the knot. Ive dont this once before, i put drop of glue on but it was on the back, and didnt seal together. I did throw that one into the wall. Now i just make 100% sure i get the glue on the crossing of the knot. Not saying this was what happened with you, but i have seen it happen before, and after looking closely at the glue i saw it was only on one side.
Also its possible that the glue you used may had been aged, or maybe going bad. Or maybe it was just the wrong kind of glue. Im not sure /shrug 
Maybe try to find a flexible curing CA. or try Bondic (UV cure plastic weld) or something similar.