I also have this specific issue, only changed out the battery (didn't even remove the screen), and then both cameras, torch and earpiece speaker ceased working.

I have inspected ribbons/connectors and all appear fine,

Have just undergone DFU restore to no avail,

Suspected motherboard damage, but I don't know how this could have happened.

Edit: Opening the phone, the rear camera/torch works, then ceases once the phone is closed again.

Further proving my below suspicion that the front camera ribbon is the culprit.