Gallery Display Problem On Mobile

Hello,
On our site http://kr-events.co.uk/krevents/photo-gallery/
when the photos are viewed on a mobile phone and you zoom in on the photos; the zoomed in photo is actually smaller and does not fit the display size. (Especially when turning to landscape mode, it isn’t being responsive and fill the whole screen as you’d expect)

Also, completely randomly, some photos are missing and when you zoom in on others just a white box appears as if the zoom in script was stuck.
On refresh the problem goes away on the affected photos and affects others instead.

Please advise, thank you.
Many thanks,
Lee