The reason you lost money today is abusive short selling on ETF's containing the S&P Small Cap 600.
The ETF's were used to indirectly short another company in this index, so the short sellers bought all other stocks in the ETF including $COKE...
So when $COKE left the index today, the short sellers had to get rid of these additional stakes in $COKE at all cost.
This created the massive sellof you experienced.
By the way: $COKE was replaced by $GRBK Green Brick Partners in the index, which rose about 9% today...