Uploaded files not showing instantly as a preview

When files are uploaded through the media modal ordinarily the uploaded file will then instantly show as a preview in the media library pane with the most recently uploaded file selected and it’s attachment details pane showing on the right.

The problem that I’m seeing is that when I upload an image it’s not showing the preview instantly in the gallery pane.

When you upload your initial images to the post there isn’t a problem. It’s only once you re-visit that post and try upload further images that the image doesn’t show in the gallery pane. If you then refresh that browser window/tab and try and insert media again that you see the images did upload to the gallery (they just didn’t display in the gallery until the page was refreshed).

There is no error message and the images seem to upload successfully as indicated in the area where the attachment details display on the right. it’s just the preview that doesn’t show.

Ordinarily as soon as you click the upload button your files will show in a placeholder in the gallery with a progress indicator which will then show a thumbnail of the image once upload is complete. It’s as if the media modal decides right away that it’s not going to show a preview because it doesn’t even show the placeholder with progress indicator.

This happens regardless of post status.

It does not happen with post/pages it only happens with a custom post type.

This happens regardless of user level, even admins have the same problem.

Has anyone got an idea what might be going on here?