I have a similar issue. I am using the ggplotly() function in order to convert from ggplot() to plotly(). First i make a plot of two geom_area() with the same data.frame but different columns, then wrap it inside the ggplotly() and for the positive side it shows the text when hover, but in the negative side shows the labels but with no value.
I have google it and still no answer or possible reason, any guidance will be appreciated.