I had a problem where after installing the new display assembly from iFixit (which included new front facing camera and sensor cables) my front facing mic and ambient sensor were not working. I could not talk on speakerphone or to Siri and Auto-brightness stopped working. From some of the forums it seems there is some slight difference between the 5S and SE assemblies and iFixit is selling the same one for both. I went through three replacements from iFixit, all with the exact same problem. I finally fixed it my transferring the front camera and sensor cables from my old (original) assembly to the new one from iFixit. Everything works again. If you have the same problem, I would transfer the Front Facing Camera and Sensor Cable before going through the hassle of getting replacements.
This is much easier to do using a plastic card. Just slide the card under the side of the battery and rock it back and forth. The battery will separate pretty quickly with minimal residue.