The "Combine nearby posts" option displays clusters where there are None

[this-statement-is-false]

Hi there,
I am running my own deployment of Ushahidi, using the latest version:

https://github.com/ushahidi/platform-release/releases/tag/v6.0.0

When I tick the checkbox "Combine nearby posts" I see that the posts are clustered on the map.
However I also see that sometimes when there is only one post in a location, Ushahidi displays it as a cluster of 2.

In the above screenshot you can see a cluster of 2, which I can expand to show two post icons. However these are the same post.
I have exported the data and double-checked to make sure that there is no duplicate data.

I am not sure if the following settings a relevant, but I am supplying them to you just in case:
Default base layer: Streets
Default zoom level: 16
Map Precision Level: 2