1. Delete and re-install the app.
2. Restart all devices: modems, routers, phones, tv's, computers, laptops, tablets, etc.
3. Clean cache and clear browsing history on web browsers and restart your computer.
4. Reset password (for people who cannot log in) If this does not go to your email then there is a chance that you misspelled your username/email upon signup.
5. Update your device's software to the current version.
6. Make sure that all of your devices are on the same WIFI network. Many homes now have different speeds. For example: 2.4ghz vs 5.0ghz. All devices trying to connect have to be on the same network.