After a series of adjustments to my December high probability option trade portfolio, its P&L chart does not look really smooth anymore. The red expiration curve shows more profits if price goes higher by 10 or more SPX points while the portfolio delta is -26 which indicates more profits if price goes lower. So I studied its Greeks verse time and prices using the ThinkOrSwim Analyzer.
First, let's take a look at how Delta changes as days get closer to expiration and prices fluctuates . After analyzing the delta changes in time, I found my delta would continue to go more negative in the next few days and it would start to increase only in the last 7 days to expiration as shown in the image below. The daily delta changes would be smaller if price increases to 1423 vicinity. I think it is most likely caused by the butterfly spreads that the portfolio has.