Huge difference in option price previous day and today

YESTERDAY I SAW COAL INDIA WA TRADING AT 392 AND COAL INDIA 390 PUT OPTION PRICE WAS AT 19.75 AT THAT TIME COAL INDIA GOING DOWN TO 386 CLOSES AT 395 AND 390 PUT OPTION PRICE WAS AT 20.55 . TODAY COAL INDIA OPEN LOW AT 373 AND 390 PUT OPTION OPENS AT 18 MY QUESTION IS WHEN TODAY COAL INDIA OPENS AT 373 WHY 390 PUT OPTION WHICH IS NOW IN THE MONEY OPENS AT LOW FROM YESTERDAY PRICE ?? PLEASE PREFER TO COAL INDIA CHART IF U SOMEHOW MY QUESTION IS LITTLE UNCLEAR AND THE 390 PUT OPTION IS FOR MARCH 26

CIL paid an interim dividend of Rs.20.7 …and it went ex dividend today. Hence this difference.