Please refer to the figure below, the graph is of European-style options of call side IV and put side IV at the same strike and same expiry. The graph is not of some stock but of an index. Also, this index trades in Futures too. And big players or market makers are highly active in this index. The graph is of 1 day from morning to the end time of the market, 6 hours and 15 minutes to be exact. IV is calculated by the actual traded price, not by the bid-ask data as the market was highly liquid.
During the time, when the market was around the middle of the graph, the market was moving very near to the strike price of the graph. But the put IV was increasing and the call IV was decreasing. This is not expected to happen according to the concept of the put-call ratio. Please explain what may be the possible reasons for this kind of movement.
Also, after the middle time market moved downwards.