I replaced my first iPhone 7 screen and although it tested OK straight from the box when I came to the full install it was very slow to boot and then went into boot loop. The Apple symbol showed for about 10secs and then seemed to die but came on again repeatedly. I disassembled, ++including disconnecting the Home button++, reconnected the digit and LCD flexes and again it tested fine. Reassembled everything but this time I more carefully reseated the Home button and this time all worked 100%.