Since I got Minecraft, which was around May 2020, I've been having a problem where on most servers I enter, if my hunger bar is full, after around 8-18 seconds, my hunger will return to missing one and a half bars. This has resulted in many deaths including on my seven-month hardcore world.
The first one and a half hunger bars are needed to regenerate health, so if you get damage, you lose those bars very quickly, especially since the new saturation system(introduced in 1.9, I believe).
Just use a Shield and watch your hunger and you are good to go.