gallery slideshow not working after upgrade to 4.5

Good morning,
i have made multiple posts on my website that contains galleries which i have added via the ‘add media’ & ‘create gallery’ option under posts.
In the gallery options i used to have the possibility to select specific settings such as ‘link to:’, ‘columns” ‘size’, but also a option to select ‘slideshow’. For all galleries i selected slideshow and the galleries where shown as a slideshow.

Now i have updated wP to 4.5, and i can still see all these options EXCEPT for slideshow. The galleries are also not being shown as a gallery but just in rows. The code on the post page does still have the text ‘type=slideshow’ (which i did not manually enter, but was there as a result of me selecting slideshow under options in the past i assume). But as said, the gallery is not shown as a slideshow.

I have de-activated all my plugins, with no change as a result. I have also been in contact with the developer of my theme (Soho theme from gt3themes.com), and they have had all acces to my site/wp, but say it is not related to the theme.

Could you please advise me what to do/how to change this?

best regards
Ron