After the release of iOS v8.1.1 update a few weeks ago (less than one month), today Apple iOS update rolling back the version number 8.1.2. This update comes too quickly than usual, we feel like forced to to fix certain bugs and Apple did not mention any repairs that are present in this new version.
From the information we get, the iOS 8.1.2 update fix the problem ringtone purchased in the App Store automatically deleted. If you encounter this problem, you can visit the dedicated page provided Apple to restore your ringtone.
Updates iOS v8.1.2 comes with a file size of about 30 MB (depending on the type of device). So, if you are having problems with iOS version 8.1.1 please updates your Apple device.
Source: GSMArena