Same issue here, and struggling to find an answer anywhere. Only difference in our column settings to above screenshot from original post is Plain text (instead of Enhanced), 6 lines (instead of 10) and not a required column (instead of required). Our settings are in screenshot inserted below...

And a similar screenshot of what we see (there appears to be no rhyme or reason, sometimes it's a couple of dupes, sometimes more, sometimes timestamps are the same, sometimes different)...

Weirdly, we've even seen dupes where the name of the commenter has changed (top comment below is a different name to the bottom two)...

If there is no known fix - is there a way to delete the dupes? Especially confusing with different time stamps (so we can only assume the oldest is the original)