That's another thing: these screens don't show up under notifications. Avast forces you to deal with them right then and there. So if you're actually interested, but not right now because you're in the middle of something, you click it away and it's gone. You can't get it back to read it when you have the time, and neither can you take a screenshot after the fact. It's vanished. Until the next nag.
Considering we're talking about an ad basically, this is very strange behavior. Obtrusive, unavoidable, yet fleeting.