It could be the notification scheme set for that project might not be configured to notify the expected users of those actions. To confirm or deny this I would recommend trying to use the Notification helper to test out the specific issue, action, user to better understand if Jira believes that user should have gotten a notification.
If the project is not configured in that way, the helper utility will quickly give you links you can follow to make those changes (provided your account has permissions to do so).
If the notification helper confirms they should have gotten a message, then perhaps there is some other problem preventing notifications from going out. Since you're in Jira Cloud in that case, it might help to create a support request with out Cloud team and reference your Cloud URL when doing so. That way they can investigate the details of your Cloud site to see what might be the cause here.
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