Lightboxes are displaying incorrectly

I have set up 6 Lightboxes, linked to images, via the link option on the image itself.

In the live preview, the boxes which do work (Raised a ticket for certain boxes which currently do not seem to be working - do not seem to be displaying correctly at all.

Clicking the image does bring up the Lightbox, but I have the following issues:
- The image is mostly cut off, only displaying a small portion
- The text is squashed on the left hand side, elongating the Lightbox entirely, pushing it off the edge of the screen in some cases
- Text from another, unrelated, Lightbox is being displayed in the far left of the screen. Again squashed and elongated.

Is this a known issue or have I missed something in setting these up?

Any help is appreciated!