Hi,
I have same issue here.
Only Windows 10 (1909 and 2004) security tool and avast.
If no internet, no ethernet cable connect, all is normal.
Soon ethernet cable is connected, avast memory leak starts, not stop, use all ram and swap.
Memory leak occur when try to open UI or if UI are open.
The problem happens on previous version of avast and last update (30 Sep 2020).