I have the same issue as above. For technical reasons, here are my steps. Mind you, I have been using non-OEM parts but don't have anything else to try against those parts for right now.
Cust brought in phone with broken digitizer. LCD was fine. Back housing shattered too. LCI triggered on charge dock but no signs of damage or corrosion, even in charge dock.
Swapped cust housings front and back with non-OEM part. (have NOT had issues with these parts in previous repairs, but it could be an issue).
Tested digitizer, worked fine.
Tested back camera, worked fine.
DID NOT check front camera at this time.
Cust took phone and called the next day with part of digitizer not responsive half of the time and also camera frozen on shutter.
My next steps,
Replaced digitizer with another part (from the same shipment)
Checked front and back cameras connections to logic board.
Powered up iPhone, checked back camera, working.
Pushed swap camera button to go to the front-facing, screen freezes and dims then eventually goes to shutter and waits til time-out.
Reset all settings, back camera works until pressing front-facing swap.
Cleaned connectors with bristles moistened with denatured alcohol. Checked for bends or defects in the connectors of front camera.
Checked hopper (pics in previous posts) and it is still intact.
Replaced back camera, still freezing and either dim or shutter until reset settings. Also found, using power and home until restart performs the same temp fix.
I don't have a front facing camera to experiment with and I am wary of taking the cables off any more in case they are becoming fragile from my pestering the last two days.
Apple Genius Bar is not an option as we are 4 hours from any.
Any guidance or help is much appreciated. If you need to reach me directly please email firstname.lastname@example.org