I had a same issue with 7 plus. Really gently take off the flex, heated well or not, black square tape never went in 1 piece with flex, so i take it out later and stick it back to the flex -> no ear speak. After the total mad and about 30h of assembling and disassembling i realized i have been putting the black tape directly to the gold pins under the curved flex. BUT the flex is curved and the black tape should cover the pins and the part of the curved flex as well. I do not know how is this even possible, but this worked for me with 2 x 7 plus, now its worked fine.