We recently had a customer who upgraded to Mingle 15.1 and found that their inline images were no longer appearing. The attachments were still present and when they clicked on those attachments, the images downloaded just fine, but they did not appear within the WYSIWYG editor.
We found that their images were pointing to the server name rather than the site URL. For example:
<img class="mingle-image" alt="!Test.jpg!" src="http://Server_Name/projects/Project_Name/attachments/1>
And when we changed the inline image links to point to the Site URL, the images appeared.
<img class="mingle-image" alt="!Test.jpg!" src=" http://Mingle_Site_Name/projects/Project_Name/attachments/1">
To make this a permanent change, we asked them to change the Site URL in their Mingle.properties file (located in the data directory in the config folder) from the old server name to the current site name.
If you have recently upgraded to Mingle 15.1 and are seeing a similar issue, please copy the name of your Mingle site (http://Your-Site-Name:Port_Number) into -Dmingle.siteURL in your Mingle.properties file and then restart Mingle.
If you are still having trouble, feel free to contact us at firstname.lastname@example.org and we'd be happy to help.