Bluetooth headset not working with certain apps

[lugsomi]

Hello, since my Mi 9 received MIUI version 11.0.5.0(QFAEUXM) via an OTA update, Bluetooth headsets or devices do not work with certain apps.

I am using my phone for work purposes, and I'm using a pair of Bose QC35 headphones. On top of that I have also tried a Jabra Evolve 65 headset and a JBL Flip 4 speaker. Phone calls and media work perfectly fine through the headset, but calls using Microsoft Teams and RingCentral Phone both do not work in the same way:

• Headset is connected and idle
• Headset is detected by app (I can select it as the audio device)
• Call starts
• Headset immediately gives "call ended" disconnection tone
• Sound and mic switch to phone internal speaker/mic
• Repeat happens if Bluetooth device is re-selected in the app

I have carried out a full reset on the phone, as well I have tried the headsets with different devices, I also use the same apps and versions (the latest) on other Android devices and they work fine (Pocophone and OnePlus 3). Before this MIUI version this Mi 9 also worked correctly.

Please can someone investigate? As I said, I use this phone for work purposes on the move and without these apps working with Bluetooth I'm pretty stuck. I do not wish to purchase a wired headset, if this issue is not resolved I will unfortunately need to permanently change to another device.

Current app versions:-
Teams: 1416/1.0.0.2019111505
RC Phone: 19.3.2.1.14

Best regards