There are occasions when OA blocks avast processes after a program update (as by its nature changes processes), now that is generally not a problem. What is that OA does it and doesn't say a sodding word that it has done it, so the user isn't aware of OA's interaction, just that avast or elements of it aren't working.
Most 'good' firewalls wilt notice the changed processes, etc. and pops-up a notice it has changed, you know you have recently done an avast program update, so you 'allow' it and no problem.
With OA I don't know if there is a setting that you can change to have these notifications or if this is part of its simplicity by taking decisions for the user not troubling the user with notifications, not my idea of user friendly.
Other than that there doesn't appear to be any other issues, just remember OA could do this, etc after a program update.