[OnePlus 5T  ROMs, Kernels, Recoveries, & Other Dev] srs5694:
Bluetooth problems on phone calls only

I'm having problems making bluetooth phone calls with my OnePlus 5t running LineageOS 16 on a Tesla Model 3.

I took delivery of a Tesla Model 3 on March 30 of this year. At the time, it was running Tesla's software 2019.5.15, but within a day it had upgraded to 2019.8.4, then 2019.8.5, then 2019.12.1 a few days ago, and now to 2019.12.1.1. Through all of this, I've had no problems with Bluetooth connections to my OnePlus 5t phone for media streaming; however, I have had problems with placing and receiving phone calls, and the problem has gotten worse with Tesla's 2019.12.1 or 2019.12.1.1 (I'm not sure which).

I never tried making phone calls in the day or so I had Tesla's 2019.5.15, but I did with 2019.8.x, with about a 50% success rate. Sometimes it would work fine, but other times I'd get very stuttery sound, as if the connection was cutting in and out about ten times per second. Initially, I was running LineageOS 15.1; however, in part because I hoped to resolve this problem, I updated my phone to LineageOS 16 about two weeks ago. That update did not fix the problem, unfortunately, but it also did not make it any worse.

Since my car has updated to 2019.12.1 or 2019.12.1.1, though, the problem has gotten worse: Now, when I try to place a call, at best I'll hear a brief click, short series of clicks, or beep, and then I get silence. When receiving a call, the phone rings, I hear a ring tone over the Tesla's audio system, and the Tesla's screen shows an incoming call. I can answer the call via the Tesla's screen, but again, I get no audio. Worse than all of this, sometimes, on both incoming and outgoing calls, the Tesla's screen has gone completely blank a few times. This isn't guaranteed to happen, but it's happened at least four times to me today as I've been testing things.

Some of what I've tried, with no success:

Adjusting volume settings on both the car and the phone

De-pairing the phone and the car, rebooting both, and then re-pairing them

Updating the phone to the very latest LineageOS build (lineage-16.0-20190428-nightly-dumpling-signed.zip)

Using "developer mode" Android options to adjust every Bluetooth option I could find (AVRCP version, audio codec, audio sample rate, bits per sample, channel mode [stereo vs. mono], LDAC codec)

Testing with both incoming and outgoing calls

This same phone works fine with a Bluetooth headset. On my previous car (a 2017 Chevy Volt), I had few problems, although on about 5% of the calls, I did experience the stuttering audio problem that kicked up to 50% frequency with the Tesla before it stopped working altogether.

The Tesla works fine with an LG V20 that also runs an unofficial build of LineageOS 16; however, that phone running that software is extremely buggy to the point of unusability in other respects, so switching to it is not an option.

I've gone to Tesla's Web site and used their "contact us" link to file a bug report (although there was no "bug report" option, so it may not get routed correctly).

Does anybody here have any other ideas of what I could do, short of replacing my phone or installing another Android version? (I'm really trying to avoid the pain of setting everything up again!)