problem with links in the portfolio section

Dear,

My website is getting form now, there is however a very annoying mistake that I cannot solve at the moment.

If people would scroll down in the main page and click on one of the artworks in the portfolio section, they will come on a page in this portfolio section where all other artworks from this series is lined up in a horizontal scroll section. On this page they can read the descriptions etc. and of course after finishing they would normally be able to go back by clicking on the cross in the right lower corner. However the cross just refers back to the current page that they are on (the same page in the portfolio section). This must be very annoying, does anybody knows how I can solve this problem.

Here I implement a link directly to one of the pages in the portfolio section where you can find the cross that isn’t working.
https://www.driesketels.com/portfolio/rising-universe/

I hope somebody can reply and help me with this problem, in the past I didn’t received always help on this forum which makes it sometimes very hard. Thanks in advance,

Greetings,
dries