This is related to CQ-4286779, on selecting all assets and move them from one location to another, asset UI spins indefinitely. The issue related to bulk asset move operation only occurs when there is a page or more pages have conflicting references.
<html>
<head>
<title> Error</title>
</head>
<body>
<h1> Error</h1>
<table>
<tbody>
<tr>
<td>Status</td>
<td><div id="Status">500</div></td>
</tr>
<tr>
<td>Message</td>
<td><div id="Message">One or more pages have conflicting references.</div></td> </tr> <tr> <td>Location</td> <td><a href="" id="Location"></a></td> </tr> <tr> <td>Parent Location</td> <td><a href="" id="ParentLocation"></a></td> </tr> <tr> <td>Path</td> <td><div id="Path"></div></td> </tr> <tr> <td>Referer</td> <td><a href="" id="Referer"></a></td> </tr> <tr> <td>ChangeLog</td> <td><div id="ChangeLog"><pre></pre></div></td>
</tr>
</tbody>
</table>
<p><a href="">Go Back</a></p>
<p><a href="">Modified Resource</a></p>
<p><a href="">Parent of Modified Resource</a></p> </body> </html>
Looking at CQ-4286779, it looks like the issue is fixed in internal 6.6 L20 and I am assuming its fixed in latest AEM SP. Can you test the use case in AEM 6.5.6 patch and confirm please?