Galleries lightbox not working

Hi,

I’m trying to make a lightbox gallery working for a site, and tried a lot of plugins now. Some of the other plugins I tried have this same issue:
The one I (mostly) use on sites is the gallery shortcode from Shortcodes Ultimate plugin (https://nl.ww.wp.xz.cn/plugins/shortcodes-ultimate/). This gallery works fine on sites with other themes.
What happens: The gallery is visible, the popup appears when clicking on it, but the forward / backwards arrows to scroll through the photos don’t appear.

How can I make it work woth OceanWP?

Thanks and best regards,
Kim

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