RAM-memory builds in browser and makes keyboard shortcuts stop working

Update - the shortcuts work if pressing severel times or in one case if pressed in a specific order. Ctrl+F9 works if F9 is pressed first.

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A client is having difficulties with keyboard shortcuts in a course with about 220 slides.

The problems appears at slide 151 but only if you proceed throw the course normally.

If you select the section trough the TOC it works fine.

Inspecting the course in IE11 using the F12 debugger you can see that the memory consumed keeps building up and most likely creates the issue.

Also the settings in the index.html page force the browser to use IE 10 instead of Edge (IE11) why is this?

Grateful for any help!

//Regards