Malwarebytes free doesn’t run in real time, how could it conflict with Avast?
If both are on the computer they attack each other, at least that is my experience. I did fine with Avast until I put Malwarebytes in there. Each seemed to identify the other as malware. My son all that out and loaded Mbytes with AVG and it has never given me any trouble. I have the paid versions of both now. One was 9.95 and the other was 14.99.
My son who is a bona fide qomputer whiz first installed Avast for me then later, when it got all balled up after I got Mbytes for a particular intruder that Mbytes was specified for, He cleaned up my box and said the two programs conflicted.