Content missing on front end, iframe no longer works

Hello,

I have a problem, which occurred after updating the parent theme to 4.6.1 via FTP (according to the documentation) on this website: https://www.yourvcam.com/ . Most of the content is no longer visible on the homepage (the 2 top sections), as well as the Partners page. However, the entire content appears in the back-end and if I inspect the page with the dev tools, everything seems there as well.

Another issue that came up is that on the page https://www.yourvcam.com/areas-of-application/ some iframe lightboxes used to open when clicking on one of those 4 images. Now the link is being directly followed instead, leading to other pages (which also have their content missing). I also get the .magnificPopup is not a function problem in the console, which I’ve seen others have. None of the solutions I could find for it worked.

I have tried disabling all plugins, re-installing the theme, installing the old version, updating the permalinks, updating the pages individually or creating new pages, but I run into this problem everywhere.

Please, help me with solving these problems!

Thank you very much for your time in advance!
Kind regards