I've had this issue since early May, hoping I'd get an update but the previous topic concerning the issue is now locked without a solution. So, a new one.
Spontaneously my lightboxed images appear small, instead of proportionally filling the screen space as they did before in the supersize mode. It only appears this way on desktop (Chrome, FF, and IE tested), whereas on mobile it fills the space as it should.
I have cleared all caches, messed with different Envira settings, regenerated thumbnails, updated Envira and X, and deactivated unrelated plugins... nothing seems to change. Again, this happened out of the blue, I had not changed anything Envira-related since setting it up.
Here's a screenshot, with an approximate mock-up of the space the image used to fill: https://imgur.com/BkFhV5F
And another screenshot, of the browser reduced to a smaller size vs. full screen browser, then the image enlarges to fit the screen as it should: https://imgur.com/ndlLMNr
Gallery link: http://www.juliebeloussow.com/artwork/
It also seems to lag on transitioning from one image to the next, with the previous image sitting behind the new image for a moment before disappearing. If that's related I don't know, it didn't do that before either though. Figured it might be worth mentioning.
Any help is appreciated! The gallery is integral to my website, and small "full-size" views are pointless.