I've seen that there were a bug checked as resolved in the version 1.14, but in the 1.15.2 it's still here

If i summon a fireball or a dragon fireball in minecraft 1.15.2 it starts to glitch out and in, becoming "unpunchable", yet projectiles affect the fireballs

this is the command i used, but it doesn't work properly even if i modify the direction
/summon minecraft:fireball ~ ~ ~

but a picture is worth a thousand words, so there is a short video filming the weird beaviour
(sorry for the bad english, enlgish isn't my first language)