Raid Captain never spawn in a raid

Summary:
Raid Captain never spawn in a raid.that's weird.how a raid go without raid captain.In java raid captain spawn in a raid.in bedrock raid captain never spawn in a raid.
How to Reproduce:
1.Raid captain can spawn in a raid.
2.when raid captain kill nearby illager can pickup the illager banner and become next raid captain.

1. -> but raid captain can't spawn in a raid