I am having a similar problem "reactivating" Avast Free. I've used it for many, many years without issue. I would get a pop-up telling me the one year free license was about to expire. I would click on "reactivate", get a screen that asked me to choose between "free" and "premium". I'd click on "free" and it was renewed for a year...
But this year, nothing I do will reactivate Avast Free. I get the "reactivate" screen and click "reactivate". It takes me to the "selection" screen showing "free" or "premium"... but clicking "free" does absolutely nothing. I've done this... a dozen times to no avail. I will occasionally get a pop-up window offering a one year "deal" on a premium subscription... but there is no option click "no" or to choose the free version.
I will say that even though the Avast UI says "You are not protected", I notice that the virus definitions are still updating every day. I will also note that I am using Mozilla Firefox.
How can I reactivate Avast Free for another year?