Linked smart object missing and cannot package

 
for me this problem was caused by broken references in Layer Comps. I didn't need them anymore and after deleting them everything went smooth : ) 

<p>It seems like you've taken several steps to resolve the issue with the missing linked smart object. Despite converting all smart objects to layers, filtering out linked smart objects, and embedding all smart objects, the problem persists. Since Photoshop isn't indicating which smart object is missing, try the following:</p>

<ol>

  <li>Check for any hidden layers that might still contain linked smart objects.</li>

  <li>Review any layer effects or adjusments that could be referencing the missing smart object.</li>

  <li>Try exporting the file to a different format or saving it under a new name to see if that triggers any warnings or errors that specify the missing object.</li>

</ol>

<p>If the issue persists, consider reaching out to Adobe Support for further assistance.</p>