I've done about 5 of these iPhone 7 Plus' now. Never ran into a problem besides the last one.
After putting the screen back together, customer reported ear speaker not working. I took it out, realigned it, put the flex back in, still nothing. I ended up ordering a flex front camera flex.
I took out the old flex, put in the new flex, and this time, I tried a different technique of inserting the flex connector, similar to the iPhone 6 digitizer flex. If you angle the connector, slightly angled down on the side of the flex cable, and the other side slightly angled up, then press in and connect it, you will get a proper snap in sound. After I turned it on, the ear speaker was working.
For me, i'm not sure if getting a new flex was the answer, or just the connector wasn't being placed down correctly.
On the next 7 Plus that comes in, I am going to test the old flex with my technique, and see if the ear speaker works. I'll report back after some time.