Anker Soundcore P20i (BT5.3 TWS) stutters while running.

So, I have been doing some testing. 

Sat still inside for all tests  run activity used for all tests. Watch Within 60cm of headphones. Headphones fully charged. EPIX Gen 2 Pro. Using Spotify.

when connected to watch and listening to music with no activity running there is no stuttering at 10mins

i then activate an activity without reconnecting headphones. Stuttering starts around 8 mins and is every second by 10 mins. 

I then stopped activity and reconnected headphones which appears to reset the problem. 

running an activity without gps there is no stuttering after 10 mins. 

stopping the activity and starting a new one with GPS only results in stuttering after 2-3 mins. A second test that included a headphone reconnect had stuttering at 6 mins. 

I stop the activity and reconnected headphones. With gps set to all satellites first stutter at 07:50 increasing in frequency until stuttering every second at around 10 mins 

a headphone reconnect and gps set to all sats + multi band resulted in stuttering starting at 06:50. A reconnect without stopping the activity appears to reset the stuttering for another 7 minutes

after navigating to menu>connectivity>phone and pressing light button 5 times I set BLE  PHY mode to force 1mb (default is adaptive). This was a garmin suggestion in another thread.

I then used auto gps reconnected headphones and started a new run activity. This resulted in stuttering at 09:40 

Another reset this time with BLE PHY set to prefer 2mb (the only other option)  this results in no stutter after 10mins  

I have not tried this whilst running but enabling 2mb seems to resolve the issue. This means the watch is transmitting at 2mbps but is more limited in range but has a greater throughput. Theoretically 1mb should be the more stable option but it may be due to the bitrate of Spotify downloads.  1mb must not be enough for whatever reason and adaptive is switching causing problems