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Here are a few steps you can try to resolve this:
Check Permissions: Ensure that the users have the correct permissions to view and edit the notes. Sometimes, permissions might restrict access to attachments .
Update Software: Make sure that all users are running the latest version of the Notes app and their operating systems. Compatibility issues can sometimes cause these problems.
iCloud Sync: Verify that the notes are properly synced with iCloud. Sometimes, attachments might not be fully uploaded or downloaded, causing preview issues.
Try Different Devices: Ask the users to try accessing the attachments on different devices (e.g., iPhone, iPad, Mac) to see if the issue persists across all platforms.
Reattach Files: As a last resort, try removing the attachments and reattaching them to the notes. This can sometimes resolve issues with corrupted files or incomplete uploads.
If these does not solve the issue, consider contacting Apple Support.
If this fixes the issue, please mark as resolved to help others with find it.
Happy to help
Robu 1