Play button glitch

Hi all
I have been looking into the play button glitch experienced by a student from the UK. (Thank you again for your great review by the way!).
It has taken me some time to work out the issue and apparently the buttons only partially appear on certain iPads/iOS versions. Fortunately, they are still usable but I am keen on working out a fix for this.
Please be patient and keep enjoying your playing.  
Regards,
Mario