Script error "jwplayer.volume is undefined" on IE11
I have the player working on Chrome, Firefox and Edge but I'm getting the following message on IE11;
"Unable to get property 'jwplayer.volume' of undefined or null reference"
The player fails to load and the stack trace just runs off into some minified jwplayer script I cannot debug. I've seen other questions on this but no answer beyond something about being offline (I'm not) and that it isn't reproducible.
Are there any steps I can take to check my environment to see what could be causing this? I'm worried that if IE11 is not reliable in some circumstances this would have negative customer impact.