Thank you for posting your question in the Microsoft Q&A forum.
Regarding your issue, may I kindly ask a few questions so I can understand your issue better:
- Does this issue happen when you use Teams on the web?
- Does this issue happen with other users as well?
- Were you able to create an assignment normally without adding an attachment?
- If this issue happens on Teams desktop, have you tried clearing cache yet? For more details, please refer to: Clear the Teams client cache - Microsoft Teams | Microsoft Learn
- Can you provide a screenshot of the issue in Teams for me if possible (make sure to hide all of your personal information)?
Hope to hear back from you soon.
The initial response may not fully address your needs, but it will help me better understand your situation. Once I get the information, I will try my best to find the next steps.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
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