Intermittent issue with subtitles -

I'm having some issues with subtitles not appearing in a module, but only intermittently.  We have several 5 minute videos within the course. We have multiple translations of the same module each published as separate scorm files so are testing each translation.

On each video page the subtitles are set to turn on in the variables. (Set Player.DisplayCaptions to value True when the user clicks Play_button).

Subtitles have been added using the Closed Caption feature within Storyline.

For the majority of testers the subtitles come on as expected on all videos.

However, sometimes the video loads with the cc button in the player underlined indicating that subtitles should be on, but the subtitles don't appear.

- Clicking and unclicking the cc button on the player does not work to turn the subtitles on when they haven't appeared (this button works as expected once the subtitles appear).

- Some testers found that by the end of the video the subtitles did suddenly appear without them clicking on anything.

- The subtitles will come on if the learner either leaves and returns to the video page, or completely restarts the module - however this is far from ideal.

- Usually it's only one video per module that is the problem. Once it works on one, it seems to work on all the others, but it is very intermittent. The module is translated into many languages, and there doesn't seem to be any correlation between translations about which videos the subtitles don't appear. It seems very random.

To give a scale of issue - across 40 testers it's happened 4 times. Given that we are rolling out to 40,000 - I'm concerned.

 

Has anyone had anything like this, or have any ideas given that it works the majority of the time - just occasionally doesn't?

It's the intermittent nature of the problem that confuses me. As far as I can tell the module is set up correctly, so why would it work sometimes and occasionally not work?