Dear Mr. Tuan Anh,
Allow me to apologize again and thank you so much for reporting the issue with Loop Task Lists not syncing with Microsoft To Do or Planner. I can see many users and organizations are currently experiencing problems like you. This is a known issue currently affecting multiple organizations, and Microsoft engineering is actively investigating it.
Let me assist you in documenting this situation clearly:
- Tasks assigned in Loop are not appearing in To Do or Planner.
- Red triangles or missing assignees may appear in the task list.
- The issue is not isolated, many tenants are impacted.
- Microsoft is working on a fix and improving error messages to help users identify sync failures more clearly.
I kindly encourage you to submit feedback directly to Microsoft via this link:

Your feedback is incredibly valuable. The more reports we receive from affected users, the faster this issue will be prioritized and resolved.
And I’m so appreciated to please consider mark as Answer this response so others in the community who are facing the same issue can easily find it.

Please notice and accept my apologies that as moderators in the community, we are not responsible for the product design and have limited resources for the advanced info for Microsoft products. To help you send your feedback and requirements to the related development team, we have redirected you to the correct path.
We sincerely apologize for the inconvenience and truly appreciate your patience and collaboration. Thank you again for bringing this to our attention!
Best Regards,
Vicky-I - MSFT | Microsoft Community Support Specialist