Can’t add images from media library

– WordPress Version: 4.7
– Soliloquy Lite Version: 2.5.0.8
– Exact steps taken to reproduce the issue:
1. Create a new slider or open an existing slider
2. Click the “Select Files from Other Sources” button.
3. The media gallery modal pops up as expected.
4. Select one or more photos to add from the media gallery.
5. Click the “Insert into post” button.
6. The media gallery modal disappears as expected.
7. Here’s the problem, the selected images aren’t added to the slider. Uploading images directly to the slider works, but I can’t use images that are already in the media gallery. When I click the “Insert into post” button, it makes and AJAX request that appears to complete successfully, but no image are added.
8. I’ve disabled all other plugins and tried different themes, including 2016. This problem is happening in both Firefox and Chrome. I can’t seem to add images from the media library or even generate a meaningful error message regardless of the plugins or themes (or lack thereof).
– What the error is: No error message is displayed.

Any ideas?