Control nav not showing in single portfolio

[Topic modified – adding brackets does not help you get support here for a commercial theme]

Hello!

I manage to make Flexslider control nav show when a slider is inserted into a page, like https://estudiobonanova.com.mialias.net/arquitectura-residencial/ but on in a single portfolio page it doesn’t show https://estudiobonanova.com.mialias.net/proyecto/casa-esporlas/

Actually, I had a look with Firefox 3D inspector, in both cases the controls appear under the picture, but in one case it shows and when it’s with the portfolio built-in gallery, it doesn’t… The theme used is CoWorker but by default, the control nav is off. https://themes.semicolonweb.com/wp/coworker/portfolio-item/media-player-ui/
I tried giving different z-index but nothing… Any clue would be very welcome! It’s a paid theme and they are supposed to give support, but they don’t at all :S

Thank you in advance,
Anne-Sophie