LightBox problem

I have a issue,
On my forum if somebody insert Thumbnail on the comment some times no body can see in the LightBox.
Some times just the last pictures, some times the first picures and sometimes all is OK.
Maybe do you know why?
What I have to do?

the picture witch one i see now is W:1536 H:2560
Maybe too big? But this only 1.06MB have to work.

thanks Norbert

XF 1.5.0


Well-known member
Some more information would be helpful and even some screenshots demonstrating the problem.

What exactly happens when "nobody can see them in the lightbox"? Does the lightbox even open? Does it open blank?