Hope my story is useful to fixing the subject problem: I have an iPhone 8 and recently installed free Avast security. Pulled into the same parking lot I did a month ago, that is, before I installed Avast. I have made no other changes to my iPone. Several businesses are in said parking lot, each with WiFi. Instantly an error message pops up: “Cannot verify server identity…” I press Cancel on this error message. Five seconds later it comes back - I cancel again. This happens innumerable times. I get a new phone call; however, I cannot answer it until I press Cancel. I cannot do other things on the phone either unless I press Cancel. Over and over again. This is unacceptable. Need help.
As you have Avast Mobile Security on an iPhone, your post would be better placed here:
https://forum.avast.com/index.php?board=94.0
Is your problem same as this?
https://forum.avast.com/index.php?topic=237268.0