nextgengallery singlepics and pinboard

Hi Pinboard,

I am using the NEXTGEN gallery plugin together with the Pinboard theme.
I encountered some problems when using the singlepic shortcode from the NEXTGEN gallery. I am using the fancybox effect and when I want a singlepic to “pop up”, it shows them twice, once with the fancybox effect and once with another effect, the colorbox effect. I posted a similar question on the support forum for NEXTGEN gallery and they said it might be the Pinboard theme applying the colorbox effect to these images. However its not applied to all images. To better show what I mean I will provide links to the website so you can see for yourself.
I put 4 pictures as singlepics on the website, but here comes the weird part. 1 of them works correctly, 3 of them don’t. These 3 show up twice when clicked.

I found that the link-tag of these 3 images have 2 classes in the html: ngg-fancybox and cboxElement. The 1 that works correctly only has the ngg-fancybox class.

It is hard to put in words what the problem is so here are links to my website:
first image works correctly, second doesn’t:
https://eigentijdsevastgoedstyling.nl/makelaars/

only first image is a singlepic, but it doesn’t work correctly:
https://eigentijdsevastgoedstyling.nl/particulieren/

only first image is a singlepic, but it doesn’t work correctly:
https://eigentijdsevastgoedstyling.nl/werkwijze-en-tarieven/

I already tried with different themes such as the default wordpress themes and they seem to work correctly. Also, deactivating plugins had no positive results on this problem.

If it is indeed the Pinboard theme that applies this colorbox effect, is there a way to shut it off?

I hope someone is able to help me find out what to change to make this work. If i need to provide any information, please let me know.

Thank you in advance,

David