Your PHP generates this html for gallery grid item:
<div class="sh-image-gallery-item">
<div class="sh-gallery-item">
<div class="post-meta-thumb">
<img src="https://www.coleopterafarm.cz/wp-content/uploads/2019/12/PICT9418-660x660.jpg" alt="Carabus (Coptolabrus) smaragdinus brannicki">
<a class="sh-overlay-style2" href="https://www.coleopterafarm.cz/wp-content/uploads/2019/12/PICT9418-1024x768.jpg" data-rel="lightcase:imgCollectionsh-image-gallery-simple-Bi7XU3vsdZ">
<div class="sh-overlay-item">
<div class="sh-overlay-item-open"></div>
</div>
</a>
</div>
</div>
</div>
The problem is JS script a part of bundled js file https://www.coleopterafarm.cz/wp-content/themes/jevelin/js/plugins.js expects title="your title for image"
attribute for <a class="sh-overlay-style2">
So proper HTML would be
<div class="sh-image-gallery-item">
<div class="sh-gallery-item">
<div class="post-meta-thumb">
<img src="https://www.coleopterafarm.cz/wp-content/uploads/2019/12/PICT9418-660x660.jpg" alt="Carabus (Coptolabrus) smaragdinus brannicki">
<a class="sh-overlay-style2" title="Carabus (Coptolabrus) smaragdinus brannicki" href="https://www.coleopterafarm.cz/wp-content/uploads/2019/12/PICT9418-1024x768.jpg" data-rel="lightcase:imgCollectionsh-image-gallery-simple-Bi7XU3vsdZ">
<div class="sh-overlay-item">
<div class="sh-overlay-item-open"></div>
</div>
</a>
</div>
</div>
</div>
This way JS will use title from clicked item and display it as it should.
Also it's more a question to support of Jevelin theme devs https://themeforest.net/item/jevelin-multipurpose-premium-responsive-wordpress-theme/14728833/support
Probably they've fixed it in next theme's update.
Or you'll have to alter PHP yourself.