I am having similar issues. My findings to date suggest that Piwigo may be responsive, in that it responds to differing screen sizes, but it does not adapt to HD / Retina displays. I found a helpful site at https://www.kirupa.com/html5/detecting_ … gh_dpi.htm . This explains the concept and has a demo script to show what sort of display you are working with.

On my desktop (a fully patched iMac running the Safari browser) when I am on the photo page, the form title and the text when hovering the mouse displays the original file name. I have to right click and start the 'Save image as...' dialog to see the file name of the image being displayed.

Good luck with your investigations!