Hope you are doing well and sorry for the trouble. As described when you use the Sticky note and add multiple replies, and save the document, the saved PDF only shows the first reply added.
Would you mind sharing the workflow/steps you are doing to add the comments/sticky notes to the PDF file? Also what are the steps you are doing to viewthe PDF after making the comments and saving the file? A small video of the same would be helpful to better understand the issue.
We are sorry to hear that. I have tried to add comments and replies to the Adobe Embedded API Demo link that you have shared and then saved the PDF, downloaded it and opened with Adobe Acrobat Pro DC and able to see all the comments and the replies.
Please try logout from the application and reboot the comouter once and see if that helps. Also make sure you have the latest version of the application installed. Go to Help Menu > Check for Updates and reboot the machine once.