Pandas is returning two groups for the same unique id.
There is been an issue with `groupby` in pandas when the COLUMN has mixed data types. 
See this question on stackoverflow for details: 

https://stackoverflow.com/questions/50552448/pandas-groupby-is-returning-two-groups-for-the-same-unique-id/50552528?noredirect=1#comment88120185_50552528