MetropleX I feel stupid, but I cannot figure out what you mean by this post. Since a moderator changed this thread to "solved", I guess you are giving the solution, but I can't figure it out.
I have Camera and also Open Camera, and I am having the OP's problem--I can't take photos from the lock screen despite enabling camera access on lock screen.
Also, I note that I have three camera "tiles"--Camera, Record Video, and Selfie--but they are all tied to Open Camera. I have a suspicion that if I had a camera tile tied to the Camera app, maybe I could access the lock screen?
Anyway, I cannot figure out how to "reset the defaults set for them". When I go to Settings-->Apps-->All Apps-->Open Camera, I don't see anything offering to "reset" for them, and I don't see any settings I can change related to security/permissions.
Could you give more details? Or do I just need to uninstall Open Camera?