Hi,
we are not able to reproduce it here even on the combination of reported devices and routers. But we probably finally found the source of this issue. In some cases, it is not possible to get Wi-Fi BSSID from a device. The workaround for this is to get BSSID from a list of nearby networks, which requires location permission. So could you pls try to manually enable the location permission for Avast Mobile Security, if the issue still persists? And please let us know if it really helped. Thank you.