Image uploads, but the modal doesn't update

Question

Using EE 2.8.1 with the default file field.

When uploading an image the modal changes to just have the blank modal with spinner screen (attached). It does actually upload though - but the user has to refresh the entry page to see it.

There are no image transformations on this upload directory, although there was previously and this happens on all directories.

Also, as the screenshot demonstrates no JS errors are occurring within Chrome's Web Inspector.

However Firefox's debug does show this message upon pressing "Upload File"

The character encoding of a framed document was not declared. The document may appear different if viewed without the document framing it.

Does anybody know of a fix for this?

Answer 1

It seems that setting cp_session_type to s from c solved this issue for me.

If I get more time I'll investigate a bit deeper and leave more notes in the comments.