I have encountered this issue only after updating to 1.13.x and not any version prior. All difficulties have automatic regenerating hunger, regardless of whether it is singleplayer or on a server.

Confirmed difficulties with regenerating hunger are easy, normal and hard.

For clarification, this is hunger regenerating like health does on peaceful.

Current version being used is 1.13.1 on a server, as I need worldedit to work serverside, and there is no 1.13.2 version yet.