Hi Gynele 

Thanks for reaching out in the Lucidchart Community! Just to make sure I understand the issue correctly: 

1) You have created a document and inserted a youtube video on it
2) You generated a sharable link with “View (Public)” permission.
3) You shared that link with a user.
4) The user you shared the link with is unable to play the youtube video when using the presentation mode. 

If that describes the issue accurately I’m unable to reproduce the issue you are experiencing. Users who have access to a shareable link with view only permission should be able to present the shared diagram and play any youtube videos inserted on it unless they are on free accounts. 

I’d recommend taking a look at the section "How to Insert a YouTube or Vimeo Video" of this article as well as at our Collaborate and Share article from the Lucidchart Help Center to double check that everything is properly set up from your side. If the issue persists please have the user(s) you shared the link with try opening the document and presenting it in an incognito window to see if they are able to play the youtube video. 

If those steps don't help this is likely a document specific issue and we would love to look into what might be causing this. Would you mind submitting a support ticket here with the URL to the affected document the email address of the user(s) you shared the link with and a screenshot of the issue? This will allow us to take a closer look!

The video is working now after I refreshed the page again today.

Strange since it was not working for any of the people I shared the page to in the past week even after numerous refreshing.

Seems like someone fixed something in the back end.

Thanks for your help!