UBB.threads PHP Forum Software Community Forums UBB.threads 7 Installation and Upgrade Support Attachment Manager won't close and return to topic

Just had a pro upgrade done to v7.6.1.1
The Attachment Manager comes up as full width, not a independent window. After uploading an image successfully, the "Done" button will not close the Attachment Manager and return to the post submission form. Tried it on 2 devices and 2 browsers. Clicking "Done" does nothing.

What needs to be done?