My hunger bar will have depleted to about 80%, and after eating cooked porkchop (more than enough to fill it back up) it will sometimes start depleting merely seconds afterwards while walking around or doing nothing. I'm also playing my world on Normal difficulty.
It's been like this for a while now (these last few major updates), and I remember at one point I'd have to fix it by exiting then re-entering my world. The hunger bar isn't nearly as demanding or inconsistent for me in Bedrock Edition.
Hunger not only depletes by walking, but it also depletes your saturation(and thus your hunger bar too) when regenerating