Vertical lines of overlapping points in Seaborn Swarmplot
As per the Sea born documentation, -

https://seaborn.pydata.org/generated/seaborn.swarmplot.html

"This function is similar to stripplot(), but the points are adjusted (only along the categorical axis) so that they don’t overlap. This gives a better representation of the distribution of values, 


  but it does not scale well to large numbers of observations.


This style of plot is sometimes called a “beeswarm”."

A workaround may be adjusting the figsize.