Same thing happened to me yesterday. Sent in a bug report with detail. I have my main back up devices, but this bug has happened on my iPhone, iPad and Mac. If I go to iCloud.com, I can use the Find My service without any problems. I've troubleshot for the last day, trying to figure out what could have happened, and can't figure it out. I did a restore on the iPhone and the problem still persists. I haven't reverted any software back yet. Even if I have Find My on, it shows off if I go to another device and go to settings, my profile, and select the device from the list. It always shows as Find My is turned off.