If you change your the internet router, it's possible that you may lose your connection to the camera.
In this case, it may be necessary to reset the camera, remove them from the app and restart install process.

Warning: After each reset, wait for 15 min before reinstalling

If you're facing this issue with several cameras, this could mean the problem resides somewhere else. Try contacting your internet provider in order to check the settings of your new internet router (firewall strength, security keys, open ports and Wi-Fi frequency (it must be set to 2.4GHz).