Third misaligned front camera on an iPhone 6. Anyone else have this issue?

This is extremely common. I am an independent repair tech and see dozens of iPhone 6 and 6+ every day. Almost all of them are in this condition. It is purely cosmetic, it will not impact the functionality of the camera. It is unfortunate that you have not been able to get the issue permanently resolved through Apple. There is absolutely no reason to replace the entire screen to resolve this problem - and lose your tempered glass in the process. It is a simple matter to open the phone, remove the screws that secure the front camera flex to the LCD assembly, and reseat the camera so that it is centered.

Obviously if you do this yourself or have an independent repair tech do it for you, it will void your warranty with Apple. Realistically, there isn'y any way that they could tell this was done, but if you still have your 1 year warranty or if you have Apple Care Plus, then to be 100% sure you can retain that warranty you will need to keep going through Apple's official repair channels, as frustrating as that may be. If you are no longer under warranty, then any 3rd party repair shop should be able to reposition the front facing camera for you in a matter of minutes and without replacing the entire LCD assembly.

I'm not sure - every 6s and 6s+ that is out there is still under the 1 year warranty so I do not service these devices yet for any reason but liquid damage data recovery. I've only seen a handful of them and I haven't noticed.