Charged Flight Question

[TiaTheFairy]

Hello! Players have charged and enabled flight by /flyc (The message shown in chat says Enabled). But:

1. They can fly in spawn world, but can't see the bossbar showing charge amount.
2. They can't fly in other worlds at all.
   The worldlimit is already disabled totally and players have permission cmi.command.flyc.
   I have tried de-op myself and I can fly as intended, but other players all can't.