Slider src(unknown) after migration (Pytheas theme)

Hi everyone,

Theme: Pytheas from WP Explorer (no support since it’s a free theme)

Information
Ok so a client had a live website that needed to be migrated from their hosting to mine. I have this local dev setup that connects to a VPS that is maintained by a friend.

So the first step was to copy the website to my local setup for which I used WP Migrate DB to export the database. Everything else went quite smoothly and the copy I now have running locally is exactly the same as the old live one was.

Now for the issue. We moved the domain to my hosting and went on to set the local dev version live. I used WP Migratie DB again but there is one thing that is broken.

Actual issue here
The theme Pytheas has something named ‘Collection’ which basically is a portfolio in which the client inserts text and images for a slider.
The slider is where it went wrong, because for some reason almost all the images give a src(unknown) while the href that opens the lightbox works perfectly.

<a href="https://yamahaguitars.nl/wp-content/uploads/2017/01/IMG_1910.jpg" title="img_1910" rel="prettyPhoto[portfolio_gallery]">																
    <img src="" alt="img_1910">
</a>

Link to an item that does not work:
https://yamahaguitars.nl/collection/sf-1000-2/

Link to an item that does work:
https://yamahaguitars.nl/collection/l-5a-2/

My guess would be that it is a database error and that I should simply find + replace something I haven’t yet.

All help is very much appreciated, if needed I’ll be happy to sent you the current export of the DB!

The page I need help with: [log in to see the link]