Comments are not replicated when sharing a copy with Google Classroom
One peculiarity of Google Classroom is that comments you add to a Google Doc or Slides template are not replicated when you create a unique copy of the document for each student.
And if you share a document with comment view enabled, so that all students can see the comments, then any student can resolve the comment.
Here's an article from Google's help site confirming the lack of a solution:
Fortunately, with Mote you have a great alternative:
Adding audio directions with Google Slides
Check out mote for Google Slides as a great solution for this use case.
Adding audio directions in Google Docs
Use the 'hypermote' feature to record audio instructions within the body of your document.
Read this Learn Portal article to learn more: