Inserting image in CKEditor replaces all content

[Joachim]

I just started writing a blog post. I have a 'blog_entry' template with both a 'body' and 'images' field. The 'body' field is of the Textarea (Multi-language) type using the CKEditor 'Inputfield Type'. The 'images' field is simply of the Images type.
Within the 'blog_entry' template, I (obviously?) need to upload images to the 'images' field in order to be able to insert them into my CKEditor field (using the Insert image button).

However, whenever I insert an image, everything else within the text editor is removed or replaced. Does anyone know why this would happen, or can anyone help figuring it out?

 

NB I have just updated ProcessWire, which didn't help this matter, but am currently not able to update any other modules (same issue as mentioned here). Maybe that will eventually solve things, but for now I figured it more productive to raise this issue independently.

(P.S. This is likely unrelated, but it might be worth mentioning anyway: I just tried the text editor again, and now it is completely blank, so apparently there is more going on. Even before updating ProcessWire I had installed the AdminOnSteroids module to see if that would solve things, and had configured it to use the LightWire layout for the CKEditor. Initially this worked (but didn't solve the issue), but now — possibly since updating PW — the entire CKEditor is missing/text editor field is blank. On page load I am able to discern in a flash how the editor with the contents is loaded, so apparently something is drawing over it.
Upon inspection, it seems the html <textarea> class with an id of 'Inputfield_body' has its visibility set to 'hidden', so maybe there's a script not running properly?)