compatibility issues with engage box

This module gives compatibility problems with a component that I find very necessary, the engage box (www.tassos.gr/joomla-extensions/engagebox).
I have reported the error to them and they reply saying that the problem is in the module, specifically here: JROOT/modules/mod_relateditems_xtd /Helper/ RelatedItemsXtdHelperTag.php: 435

Attached capture.
Can you provide me with a fix? Thank you
 

engage box is a component that allows you to create popup windows with modules and other joomla elements.
What I want is to show the related contents in a pop-up module. I'm doing it with another related module but I wanted to try this one because I like how it works better. And that's when the incompatibility occurs. That is, it works with other modules but not with this one

sorry for the delay in response.
You can check it in the news of this developing portal;
dev.madridactual.es
If you want I can provide you with credentials.

I am waiting. Thank you