After selecting the option Reset to Default in the Channel notification setting of Microsoft Teams, the Channel notification settings don't reflect changes made in the User notification settings.
Microsoft is researching this problem and will post more information in this article when it becomes available.
User notification settings are the default notifications used by a user's Teams client. When a new team is added or a new channel created, the notifications settings will align to the user's notification settings.
When a user changes the notification setting for a channel, this setting overrides the default user settings.
For example, a newly created or newly added team will have the same Channel mentions notification setting set in the user notification settings.
In this example, the setting overrides the user notification settings for Channel mentions.
There's an option to Reset to default in the channel notification settings. This will update the settings to mirror the current user settings. If the user notification settings are changed again, the change won't be reflected in the channel notification settings.