Not sure if it is the same problem, but I got this when I accidentally modified the path of one series to be the top level directory of all my series. i.e. C:\TV instead of C:\TV\Whatever. Not surprisingly it messed up the database (seriesid) when I subsequently did an “Update series info and scan disk” for this series as it scanned my entire directory structure and added any newly found episodes to the wrong series.
It would be nice if drone could give a warning about this, but I’m not entirely sure how.