I occasionally find the avast icon on my desktop. In all cases, I've found that its presence is tipping-me-off that something out-of-the-ordinary has happened... for example, the program has been updated to a new version, or protection is fully/partially disabled due to avast's background service not running, or avast has re-set my customized settings to their defaults.
Indeed, just this morning, I noticed that the icon appeared... and sure enough, all my customized settings had been lost, in favor of their defaults. Fortunately, I know to backup my settings, and so was easily able to restore them. But it's annoying to have this happen, even if it's just occasionally.
FWIW, I'm running the current version, v12.1.2272 , and have been happy with it so far.