Like I said "sooner or later"
Later? How long? 10 years?
No one can possibly answer that, some find problems immediately when they just bump into remnants of a previous AV. Which is why it is important to completely remove an AV before installing its replacement. Here you are doing the reverse, leaving an existing AV whilst installing another. Just stopping the resident part of an AV still has the low level drivers.
System Restore frequently messes up avast, just browse the forums to see this.
As I have said, your system your choice, we have given you the information, act on it as you see fit.