what stock is this? put call? strike? did you use the correct settlement time? It's not the time when exchange closes.
It is nothing unusual. The buyer of the option can chose not to exercise. He didn't want the shares in his account on Monday.
I've only seen it happen on small lots in a very low volume series. It was probably an AH quote you are looking at where the NBBO was straddling 17.50.
pin risk. Fear not. If the stock goes up even higher, you would be making more money. Option premium + profit from selling the stock. Count yourself lucky.
Now you are giving stock directional advice. If some negative announcement should occur he would loose money. You are a man for all seasons. You have expertise on options, on the law and now on stocks. I admire your philosophy of life right or WRONG BUT NEVER IN DOUBT.
Be careful if you sell the stock before the calls expire, then your calls would be naked. So if you ever get assigned you will be short.