Blog lightbox weird behavoiour

Hi,

I have a weird issue when I enable the Lightbox feature on images in my blog posts.  When I click on the picture it goes full screen but the page shifts up, so I can only see half of the picture open. It does affect the images in the middle of the page and below. I'm not sure if I'm describing it correctly but you can see this in my blog.

I tested it in multiple browsers and on different machines. 

https://www.cinematools.co/blog/best-encoding-settings-for-youtube-and-h264h265