Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Dear Bobo Wong,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
As per your description, we're sorry to hear that the task status in Planner does not get synced back to Loop.
Please check if changing to another network, clearing cookies in browser can help.
For your reference: Use the Planner component in Loop - Microsoft Support
If the issue still persists, we're afraid that issue could be related to the account or the tenant background service which need to be checked from the backend. As forum support, we may not have enough permission and resource to directly check the backend environment.
In this situation, we sincerely recommend you contact your Microsoft 365 administrator, follow steps in this article to create a support ticket with Online Support. The support team over there has higher permission than us, they can remotely help check the situation on your side, involve more resource to collect logs and help you do troubleshoot. This would be a more efficient way in handling this case for you.
For reference: How do I find my Microsoft 365 admin?
If the understanding above is not consistent with yours, please feel free to post back and point that.
Your understanding and patience will be highly appreciated. We hope that you are keeping safe and well!
Sincerely,
Rhoda | Microsoft Community Moderator