Problem with a plugins ExportTypes


We are two students in internship, and we create a new theme for scholar’s creation for school in Centre Val de Loire in France. This project was (before me) a tutored project with a student of computer engineer. She created a new plugin for Omeka (ver 3.1.1) called Export type. This plugin export page information with QR code, link or PDF file. But we have a problem because we can’t delete items in the administrative interface.

And secondly, the HTML code appears at the top in all the administrative pages.

We don’t have enough knowledge in PHP to solve that. Someone can explain us maybe why there are two problems or the elements that can cause this ?
Without this two difficulties, the plugins work.

Thank you for your help !