I posted some details in the main thread but I think you might need to check the change in methodology of counting impressions and clicks Google did around September this year.
They say the data before and after is not comparable anymore as they are not counting certain events below a threshold anymore.
You might need to have your own analytics to understand your traffic from now own.
This affected only reporting of placement and impressions; basically you don’t get counts for placements below the first 10 or 20 results (can’t remember which). It did not affect clicks which are measured directly regardless of how deep in the SERP they happen.
They say the data before and after is not comparable anymore as they are not counting certain events below a threshold anymore. You might need to have your own analytics to understand your traffic from now own.