3rd party bluetooth access denied after update to firmware version 53

I've got an app which talks to a 3rd party bluetooth device (https://www.attys.tech/). This app has been working just fine on the app lab since March. Now suddenly I'm getting the error message:

java.lang.SecurityException: Need android.permission.BLUETOOTH_CONNECT permission for android.content.AttributionSource@8487bd38: AdapterService getBondedDevices

My manifest file has the appropriate permissions:

uses-permission android:name="android.permission.BLUETOOTH"
uses-permission android:name="android.permission.BLUETOOTH_ADMIN"
uses-permission android:name="android.permission.BLUETOOTH_CONNECT"
uses-permission android:name="android.permission.BLUETOOTH_SCAN"

This behaviour has changed out of the blue without my intervention so I suspect that a recent firmware update has disabled bluetooth access, even with the permissions in the manifest.

This is a biofeedback app and it needs to measure the heartrate. Without the bluetooth connection it's pretty much useless. I'm giving a demo in front of people this Thursday. This looks like a serious bug. Even if I run the app straight from Android studio it won't let me connect to my Attys.