[Nexus 6P Q&A, Help & Troubleshooting] nav13eh:
I apologize if this ends up being long winded, I want to lay out all the details.

So I recently purchased (what I had believed to be) second hand Nexus 6P. It is in perfect physical condition however, no signs of ever being used. Battery is great, performance is great, speakers are great, camera amazing, and screen is perfect. However two odd things started to occur which I believe stems from the same issue. When hanging up phone calls the hanging up process would hang for a long while and either eventually hang up or the system would soft reboot. After reboot notifications are still set to priority only "call management", although it is easy to adjust and bring it out of that. However no audio/mic works at all (Play Music and YouTube give an error that they cannot play). No audio from speaker, or from headphone jack. I could however connect to a Bluetooth speaker and audio plays just fine. I then went to do a proper shutdown of the phone (using the power button menu), and when I manually booted it back up all audio works find again. I plug in headphones and start listening to music on Play Music. After a while however, playback fails and all the audio on the phone is once again dead...queue soft reboot. And repeat the whole process again. If I'm listening to headphones and I do anything to activate the microphone, audio crashes and go through the whole process again.

So I decided to make sure it was all up to date all the way to OTA 7.1.2. Once I did and I tested, the same issues above occurred over time. So then I thought maybe if I used Nexus Root Toolkit and did a full manual wipe and reinstall of 7.1.2 factory image from Google. Phone issue initially went away, but audio playback through headphones persisted and eventually the phone issue manifested itself again.

Today I decided that I do a full wipe again and try and install Pure Nexus 7.1.2, non rooted with BeanGapps and vender image (following the entire process here to a T.) I have not been able to replicate phone issues, however the audio playback and headphones issues are easily repeatable.

TL;DR - So this leaves me with a few things;

1. I can use the phone by never connecting it to external audio source perfectly fine, no problems at all.

2. Phones calls may sometimes get stuck at hanging up, and the result is a crashed audio system.

3. The only way to temporarily solve this issues is to shutdown via holding down lock button and Power-off using the menu that appears. And then manually starting the phone back up again.

So I'm not sure if this is a hardware or software issue. The fact that it persists between full wipes and reinstall of different roms makes me think it to be hardware. Although the temporarily fix of proper shutdown and manually start back up makes me think the OS/Kernal is somehow "clearing a buffer" or something in it's proper shutdown process. Which without doing leads to the audio system being completely down. Therefore on soft/dirty reboots the audio system is still down.

As an added bonus my sim card was a Micro SIM, before I opted to take the scissors to it instead of buying a nano sim. It works (so I thought), it just doesn't fit in the tray quite right. I tested recently with a proper nano sim from a different phone, and everything worked perfect. Then I swapped my franken sim back in and...it worked perfectly fine.

I did search for this issues in previous posts but all I could find was this. The issue (s)he describes is exactly the same issue as me, but his/her solution does not seemed to have worked. I am inclined to try doing a full wipe again and flashing completely stock older version though.

Any help, suggestions, etc are greatly appreciated. And thanks to the developers of Pure Nexus, it seems to be very polished and I'd love to use it daily driver.