Heex performs html validation and there were few bugs in its html validation. You might be experiencing this bug:
https://github.com/phoenixframework/phoenix_live_view/issues/1656
Check the version of phoenix_live_view you are using. Upgrading to the latest {:phoenix_live_view, "~> 0.17.6"} will help - many html validation bugs have been fixed in recent releases.
If problem still exists after upgrading to latest - log a bug on phoenix_live_view repository.
Previous discussion in the forum:
