Locked out of iPhone for 8 hours?

Yesterday morning I woke up to a black screen with a message that said I was locked out of my phone for 8 hours. I received this once before recently, but for 10 minutes. Is this new? What caused this? It was hard to get in contact with anyone given two factor authentication generally requires a phone. The first rep I spoke to said I was not hacked, but yet they had never heard of this so how could they say for certain? I want to know what caused this? Anyone know?