Chosen Solution
After replacing my iPhone 7 Plus front screen with a preassembled front screen with camera/speaker, the front camera does not function for any third party apps and will not take videos with the self camera.. when swapping in the OEM camera/cable, it functions as it should.
Sounds like it is a faulty replacement front camera and sensor flex cable that came with the replacement screen. Try using the original camera and flex cable assembly that came from the iPhone instead. Hope this helps (:
