Some of the latest Sony TVs are based on Android TV as the operating system of the TV. Sometimes, some of the services running on the TV, under Android, stop working. The only way to resolve that is to do a full power cycle reboot on the TV. (power plug out of the wall, wait 5 seconds and back in again).
After that, the services will start again and you can use the Mirror for Sony TV app to connect to the TV.