Inline edit boxes not saving code

When trying to add inline css or js code via the pop-up light boxes, when they are closed, the code is not saved and the inline box becomes unusable. After entering inline code and doing a save, when reopening the inline editor box, it is just a blank white lightbox with no text field. Any ideas what the issue could be? Note: Code works if added as an uploaded file. https://wordpress.org/plugins/specific-files-for-posts-and-pages/ Can confirm the same is happening to me in the latest WordPress- any way to fix it?