Broken pipes are almost completely unavoidable. All pipes have a shelf life. Some are just far shorter than others. Nature takes its toll on all things in and on the earth. Even the best pipes are not exempt. Aside from nature, there is the human element under the titles on this site. All broken pipes should be replaced or repaired.
Offset are formed several different ways. Some known ways are the settling of a property, a shifting of the earth via trimmers and the like and heavy vehicle driving on top of the earth just above the pipe. The larger the offset, the smaller the pipe is at that location and the greater the chance of a backup.