Hello Th0r0ugh,
Thank you for using Apple Support Communities and for sharing these details with us. You’ve done a tremendous job in troubleshooting this very unique issue. It does sound like you’ve pretty much covered all possible steps. The last option would be test this issue after restoring your device. This step will help isolate a possible software related issue. But this step does require you to restore back to factory settings. You’ll just need to ensure that you create a backup of your data prior to restoring your iPhone. This will ensure that all your data is safe and secure. Steps can be found below:
1.) How to back up your iPhone, iPad, and iPod touch - Apple Support
2.) Restore your iPhone, iPad, or iPod to factory settings - Apple Support
If you confirm this issue continues to occur after a restore or maybe you don't feel comfortable performing these steps, you can always reach out to Apple Support. They can investigate this issue further with you. Use this link to reach them: Get Support
If you do complete the restore, you can always restore your data back on to your device by following these steps here: Restore your iPhone, iPad, or iPod touch from a backup - Apple Support
We hope this helps out. Thank you for using Apple Support Communities. Take care.