Course doesn't work reliably on iPad

Hi - I have a very straight-forward course that performs erratically on an iPad. We are not using the player, as the client is using an LMS (I was testing it via ScormCloud to make sure that the scorm tracking is working), so it's HTML5 output. It's been developed in SL2 latest update  and we've tested on a variety of iPads running iOS 8 (8.0, 8.2, 8.3). Some work fine, others find that the quizzes don't respond reliably - either the button showing the correct answer doesn't appear or the course stalls.

Is there a likely culprit to start with? Where should I troubleshoot to try to narrow down the problem? Any insight would be helpful.

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