I've been using a line graph which charts 2 sets of monthly data from Feb. 2009 to Oct. 2018 which has functioned normally without . For some reason, it is now inserting a phantom data point for Sept.'18 which results in the following:

When I hover over the bad data point, it is showing a value of 0.50% when the actual value is 20.05%.

Any thoughts on potential source or how to fix it?