Steps to reproduce:

1. Place/find a trial spawner down in Bedrock and Java editions
2. Drink an Ominous Bottle or give yourself the trial omen effect
3. Switch into Survival mode if not in it already
4. Compare the particles that appear when beginning an ominous trial

Observed result:
Bedrock Edition is missing the blue flame particles around the player when an ominous trial begins. Blue flame particles around the ominous spawner are delayed compared to the blue skull particles.

Expected result:
Blue flame particles spawn around the player and the ominous trial spawner simultaneously alongside the blue skull particles when an ominous trial begins.

Original description:
On Minecraft bedrock the only particles you see when a regular trial spawner turns into an ominous trial spawner is the potion particles but on Minecraft Java there is also a custom activation particle (like the regular trial spawner’s activation particles but blue), some blue flame particles that the player emits, and some more blue flame particles that the ominous trial spawner emits before it starts spawning mobs.