This question already has an answer here:
Two mutual funds I follow both plummeted on the same day that they paid out their annual dividends and capital gain distributions. (The rest of the year was relatively stable.) The timing seems too coincidental -- is there a standard/natural reason why this sort of drop might happen on "dividend day"?
The funds are FLVCX (dropped 27% on 2016-12-02) and NBSSX (dropped 9% on 2016-12-16).
Note that a sudden price drop on "dividend day" can be good for investors if they are reinvesting dividends: the lower the share price on that day, the larger number of shares they receive.