3 Loading dots when viewing a storyline project

Is anyone else having the same issue? A previously working storyline product now keeps stopping on random slides when previewing and published. The screen goes dim and the three white loading dots appear and everything is frozen. It must then be closed down and the learner can not progress. The learning is very simple with buttons for next and previous slides.

I have copied the images over to a new document and re-created the buttons and triggers - still pausing. I have tried on a personal laptop instead of a work laptop - still pausing. I have moved the slides around and the fault still happens on different slides. I have reviewed other training and all working fine. 

There are no hotspots, which previous posts have confirmed causes this. I haven't changed any settings. PLEASE can someone help as I think I'm going mad..... Thanks