Do you have comodo defence + or its HIPS (whatever it is called enabled ?
If so try disabling that.

Does the comodo firewall allow full ‘trusted’ status to avastui.exe (as this would have changed in the avast 9.0 update ?
If it does, try deleting the avastui.exe entry and reboot, hopefully this would force comodo to ask permission. You would obviously have to have comodo settings to Ask rather than take autonomous action.

Does comodo have a learning/training mode setting ?
If so try enabling that and see if it subsequently allows it.

Aside from MBAM do you have any other security programs ?

Sorry that’s me for the night, 1:50am here in the UK.