Marco, we’ll figure it out.
First question – you say your selector is rel=”lightbox”. This is a deprecated method, since RL 1.6 we’re using data-rel=”lightbox” and data-rel=”lightbox-gallery-n” for galleries (where n is the unique gallery id).
As you have rel=”lightbox” i assume you added this in your theme manually – please change that accordingly.
Second question – lightgallery provides a separate option for the caption (the title option is in the RL settings). Do you have that set?
Any chance to have a look at your site in on a remote dev server shortly?