Does the issue occur in the Teams web client?
If the issue only occurs in the Teams desktop client, try clearing the Teams cache and updating Teams to the latest version.
Additionally, on Teams desktop and web, specific notification types can be selectively enabled or disabled under settings under Viva Connections > Notifications and activity, please ensure your settings have not been modified.
Finally, please make sure your Teams status. If your status is Do not disturb, you may not receive notifications from activities.
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