Force closing Grindr is the most basic (and effective) troubleshooting step, and will refresh the app data on your device in addition to resetting your connection to our servers. Give it a try if Grindr's having sign-on or connection issues. 

Apple

1. From the Home screen, double-click the Home button to view the multitasking bar
2. Tap and hold Grindr
3. When it wobbles, tap the red (-)

More serious issues may require that you reinstall Grindr to your device.