Issue was already posted and closed for not being possible to reproduce. MCPE-47573

Method 1:

1. Create an entity with a minecraft:tick_world component.
2. Spawn it into the world, then save and exit the map.
3. Change the entity's identifier (make sure to change all instances).
4. When loading back into the map, the entity will be gone, but its ticking area will be left behind permanently.

Method 2:

1. Create an entity with a minecraft:tick_world component.
2. Spawn it into the world, then save and exit the map.
3. Remove the minecraft:tick_world component.
4. Kill or despawn the entity. Ticking area is left behind.

Ticking areas are fully functioning and are not listed by /tickingarea.