Hi Tomasz Grzechnik,
Thank you for reaching out, and I am sorry for the inconvenience.
The issue is related to an override of the 'image' addon in the shaper_kidzy template. However, the latest update of the template has resolved this issue.
In the meantime, you can resolve the problem by renaming the file site.php to __site.php in the following directory:
JROOT/templates/shaper_kidzy/sppagebuilder/addons/image/site.php
Alternatively, if you would like us to fix the overridden addon, please provide Joomla admin access to the hidden content section, and we will address the issue for you.
Note: Please keep full site backup before any update.
Best regards