It is possible that the Bluetooth signal is competing with other Bluetooth devices in your environment. Try setting the "Call audio routing" on "Always Hearing Device" if it is currently on "Automatic." You can find this setting under Accessibility and Hearing Devices.
If that does not solve the problem, I would forget the pairing of your hearing aids on your iPhone and then reboot the iPhone before pairing the hearing aids again.
The newest IOS 13 has Bluetooth issues. I found a workaround that usually works for all brands of hearing aids with Bluetooth.
Unpair your aids (Settings, Accessibility, scroll to hearing aids tap on your name and scroll to bottom and "Forget this device"
Back out and delete the app.
Restart phone and open battery doors of the hearing aids, or turn off aids if they are rechargeable
Reinstall app, DO NOT OPEN APP!
Pair your hearing aids by turning them on when you get to the pairing menu under accessibility menu.
once paired, your name should be blue on the hearing devices menu.
now you can follow the instructions to pair again with the software.
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