Since an Avast update a few month ago, every new Avast popups (wifi connection, application authorized by firewall…) stay indefinitely open and I have to close them manually (clicking on the “X” icon at the top right corner of the popup).
However the options indicate to close them after a few seconds.
Two Avast update versions and Windows 10 update from 1709 to 1803 didn’t fix it.
Try the following. Repair Avast:
Control Panel> Program and Features (Add/remove program)>Select Avast> Select Repair. Reboot when completed https://www.avast.com/faq.php?article=AVKB204