Hi Leon,
I have experienced exactly the same problem. I had not found your post before and I opened a thread under the Calibre forum.
Maybe the two threads should be merged. I don't know how to do it. By default, here is the link to the other thread:
https://www.mobileread.com/forums/sho...d.php?t=230702
The only soluiton I have found has been to delete the newspaper from the reader and transfer it again from Calibre.
I have not identified what triggers the appearance of the [Table of Contents] button. Do you?
Cheers, don't feel alone!