I see. It is as I expected it – between the link and the image there is a line break and spaces, therefore the plugin does not “see” the image:
<a href="https://workspace.hendersonwebdesign.nl/wp-content/uploads/2018/11/mountains-2186075_1920.jpg" data-elementor-open-lightbox="default">
<img width="1024" height="683" src="https://workspace.hendersonwebdesign.nl/wp-content/uploads/2018/11/mountains-2186075_1920-1024x683.jpg" class="attachment-large size-large" alt="" srcset="https://workspace.hendersonwebdesign.nl/wp-content/uploads/2018/11/mountains-2186075_1920-1024x683.jpg 1024w, https://workspace.hendersonwebdesign.nl/wp-content/uploads/2018/11/mountains-2186075_1920-300x200.jpg 300w, https://workspace.hendersonwebdesign.nl/wp-content/uploads/2018/11/mountains-2186075_1920-768x512.jpg 768w" sizes="(max-width: 1024px) 100vw, 1024px" /> </a>
I’ll try to fix this with the next update.