Mising Add new slide button in Course Presentation

I have installed Opigno distribution opigno_lms 8.x-2.15 It have Opigno Course 8.x-1.5 module enclosed. At this moment this is the last version of this module. Adding an activity of Course Presentation I can work in the first slide, but the Add slide button is missing. So, it's not possible to add more than one slide. Only the first button is present. All other are missing at bottom. They are marked in red in the example image. Please let me know if I have to update or upload something additional to make it work. Thanks