Custom entities do not swim under water

I tried to make a custom fish for my mod, but it doesn't swim underwater making it practically motionless at spawn. I checked all the boxes of "water entity" and in the AI of the mob I put the procedure "swim randomly". I also tried giving a dolphin grace effect to the mob but it still didn't work. However, I would add that putting the mob as hostile to the player, so that it follows him, it swims normally, but as soon as you go into creative it blocks as before. It may also be my mistake but I have checked many guides online and on the mcreator site itself and I have not yet found a solution to the problem.