From two days ago (Thursday 13 February 2020), all the windows opened during the previous session open hidden in the background and permanently unusable (unless someone solves the problem without causing the permanent loss of these windows) except the window that was active at the end of the previous session, which is the only one to open normally visible and usable.
(I can hear the audio of two Youtube videos that are in those unusable windows in the background and start automatically)
(in my settings, in the "at startup" section, "Automatically start Avast Secure Browser at computer startup" is selected, while in the "new session" section are selected both "continue where you were left" and "open the New Tab window")
("broken" windows have no more video output but they have still audio output; I want to have their video output again working, avoiding a permanent lost of them)