[Gameplay] Dragon Soul does not apply sometimes

During our ranked game on 12/10/2019 we got all 4 dragons, but we didn't receive the dragon soul buff. Even if all 4 dragon boxes were enabled on scoreboard.

We waited until elder spawned and killed it, and that triggered the dragon soul on top of elder dragon buff. Look at link provided, in chat box, you can clearly see elder is gotten at the same time as dragon soul.