I rebooted my computer and immediately got a pop up screen from Avast (??) telling me it detected a new network and "I should choose the appropriate firewall mode for the new network".
This is a genuine avast firewall popup

The other episode sound strange…could be from a rogue

Check your comp for malware with this

Malwarebytes Anti-Malware 1.50.1 http://filehippo.com/download_malwarebytes_anti_malware/
always update the program so you have latest database before you scan
click the remove selected button to quarantine any infections found

If anything is found, please post/attach the scan log here