It's been happening to me occasionally for the past few weeks. Not all the time, but probably more often than not.
It's not just with story comments that it's happening, but also for forum comments.
The annoying thing is that if I don't spot it when it happens, and then try to make comments to other posts in the same forum, I find the comment box has my previous comment still in it, and even if I delete it out, I can't post a new comment. The Submit Reply button isn't available, instead the Editor still claims that it is trying to save the comment. The only solution seems to be to refresh my browser, as a few other posters have already said in this thread.
I'm using Google Chrome [Version 75.0.3770.100 (Official Build) (64-bit)] on Windows 8.1 [with all available security updates installed].
Below is a screenshot I took last Sunday showing an example of this problem.
As can be seen, my comment has already been posted, but the comment is still shown as being saved in the Editor box.