We have comments enabled on site pages. We're seeing duplicate comments. We had similar behavior back in december.
This happens if you go to site page from news webpart. And if you open the site page in a new window/tab or refresh the page, we don't see duplicate comments.
Please see below from production tenant. As highlighted, count is accurate but I think its getting rendered twice.

Browser inspect

Please let me know if you need additional info.
Thank you for your time !
Thank you for reporting this issue. We will be triaging your incoming issue as soon as possible.
Hi - Any update, please ?
We have the same issue on several customers. For some this is a major issue. Are there any update on this ?
We have the same issue, too. Just for Info... please fix it.
This issue has been automatically marked as stale because it has marked as requiring author feedback but has not had any activity for 7 days. It will be closed if no further activity occurs within next 7 days of this comment. Thank you for your contributions to SharePoint Developer activities.
Update from MS Support Engineer "identified a code issue that was introduced in a recent SharePoint Online update. Reverted the change and deployed a fix to mitigate the issue."
This issue is resolved on our tenant.
I noticed this comment-duplication issue for the first time in our Tenant yesterday (13 June 2019). Has this issue been re-introduced or is the fix still in the deployment process?
I have one customer that are facing this issue as well. They are using modern pages and only standard web parts. No custom code.
The duplicated comments are a big issue to them as they are trying to push end users to comment on all the news pages. Let me know if you need URL's or anything to troubleshoot and see the problem.
Issues that have been closed & had no follow-up activity for at least 7 days are automatically locked. Please refer to our wiki for more details, including how to remediate this action if you feel this was done prematurely or in error: Issue List: Our approach to locked issues
Most helpful comment
We have the same issue, too. Just for Info... please fix it.