There seems to be a bug with what the black hover info tooltip does when a scatterplot chart has multiple series. With just 1 series of data it works fine, as expected.
With multiple series it darts around randomly, although it shows the same value. All additional data series have
where the original series has
With the plot having
I have found that a workaround is to change hoverinfo: “none” to hoverinfo: “skip”, but to me this seems like a workaround rather than a solution.