First of all, we appreciate you being an Avast customer and I apologize for any trouble here.
This may be related to the Windows Defender Action Center. Do you see an option in Malwarebytes to "never register Malwarebytes in the Windows Action Center?" This may resolve the conflict and allow Avast to become your "primary" AV -- as far as Windows is concerned, anyway
Both would still be running.
If that doesn't help, try running an online repair of Avast (Control Panel -> Programs -> Highlight Avast and change -> Select Online Repair then reboot)
If the problems persist after that, please reach out to support -- since you are a Premier customer, you can submit a ticket directly:
https/support.avast.com/en-us