Loading Spinner not showing on published TinCan Api on Andriod device

I have created some Articulate Storyline courses for a client. And have published the course out as SCORM Tin Can Api format. The client has reported back to us that the initial loading spinner appears at the beginning but throughout the course the loading spinner does not appear in between slides. And there a long pause in between.  This is happening when using a Android phone.  

By any chance do you have any ideas what has gone wrong? As the loading spinner works fine on iPhone and desktop. 

Thanks

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