Why does the search field appear on the lock screen?

Hi all. I've only seen this since IOS 11.1 and I don't know how this happens. Sometimes, my lock screen will just show the search field, tapping cancel does nothing. I can get this to go away only by turning off, then the phone back on again. Someone else had asked, I never got confirmation if this is a bug. I have search suggestions off with siri. Earlier versions of ios had this turned on and the search field never did show up. If anyone knows if this is a bug, please let me know. Hoping it's fixed in the next version.