Mobile Navigation menu shoots off to the right on certain pages

Site URL: https://www.simonennals.com/gallery

I have 3 pages on my website that are galleries. Buttons on the home page link to these. 

They were working fine on mobile and I haven't actually changed the two pages where this now doesn't work. I just added the buttons on the home screen and added the 'Video' gallery. 

However now on mobile the 3 dots used for the navigation menu don't sit in view on the Landscape and Commercial page. For some reason they shoot off to the right. The top bar acts as if it's on a full screen whilst the rest resizes to work properly on mobile. 

Does anyone have any idea why it would start doing this? I've tried a bunch of editing things slightly to see if it would reset itself but I haven't actually done anything for this to happen originally!

In the images you can see what it should look like, then how the page loads (without the three dots in view) and also what you see if you zoom out on mobile. 

Thanks for any help! 

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