Background and buttons appear late on the slides

I published the course created on storyline 3 in the LMS and when the users take this training, the backgrounds and the buttons appear late on slides. The rest of the content appear as set on the timeline, however, its the background that takes 2 seconds to appear although its set to appear from the beginning of the timeline and the buttons appear transparent. 

I'm attaching a few videos of this behavior. Any help will be appreciated.

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