Sorry I'm not familiar with this snap to function or if avast complies to it, outside of snap to, you can only reduce the size of avast to a certain size.
So I suspect that this may be the issue the snap to 50% may be lower than the minimum avastUI size, so if that is the case it would be a bug, but I don't know if it would be that easy to resolve.
Personally I have always said the UI is too big and I would like to reduce it to smaller than what is currently allowed.