Plugin settings note being read in

Problem/Motivation

I have just installed the module on a Drupal 8 site and followed all the instructions.
The module is working in my CKEDitor but, it does not read the settings for the link correctly and does not use the 'Read more' and 'Read less' text configuration.

Consequently, what I see when it is in use it is the 'teaser' text showing and an 'undefined' link...

Also, I cannot see any simple config items in the config table when looking into the database.

Thanks