When using send_event, if you omit the sequence or leave it empty, Minecraft hard crashes. If you have "base_delay" and/or "event" it doesn't crash.

In 1.1 you could omit the sequence and filter to use the particle effect. Presumably not defining a filter and event should save resources?

I could understand if event was required, but the fact that it works even if you only define base_delay (with no event) doesn't feel like it's working as intended.

I attached a working and broken skeleton.json for testing.