Edit: After more experimenting, I have narrowed down the bug to something more re-creatable. Fireballs cannot be punched ~100 blocks from your starting spawn. I'm not sure, but it seems to be about the coordinates {-100,-100} to {100, 100} on every world. The area you can punch them is a big square area around your usual spawn. Moving the world spawn does not change this box. Spawning in a new world and teleporting 1000 blocks in any direction and summoning a fireball

/summon minecraft:fireball ~ ~1 ~ {Motion:[0.0d,0.0d,0.0d],direction:[0.0d,0.0d,0.0d]}
will create the bug.

Also, some issues with fireballs flicking or disappearing when staying still.

Fireballs cannot be punched in some pre-1.14 worlds. This is very consistent on some of my worlds, even when all commands are disabled.

Fireballs also have a habit of just disappearing on these worlds while still being present.

For the uploaded world, be sure to run on a server with command blocks disabled to ensure the commands on the world don't interfere with anything. I would use a world without commands running, but this is the one that was bugging the most (even on servers with command blocks disabled).