When you apply a higher level of the bad omen effect that you already have using commands or custom potions, the Minecraft event sound "minecraft:event.mob_effect.bad_omen" does not play. However, if you apply a higher level of the bad omen effect by drinking an ominous bottle, the sound plays as expected.

Steps to reproduce

1. /effect give @s minecraft:bad_omen 999999 9

1. /effect give @s minecraft:bad_omen 999999 19

Observed: The sound played only after executing the first command and not after the second command.
Expected: The sound should also play after executing the second command.