What caused Sept 9->11, 2020 dramatic drop in OpenSky Collected Mode-S messages

What caused Sept 9->11, 2020 dramatic system-wide drop in OpenSky Collected Mode-S messages from which there has not been a full recovery?  The drop can be clearly seen in the Collected Mode-S Messages graph on the OpenSky Network Coverage and Facts page.  Official USA flight data shows NO such drop in flights/passengers occurring in September, 2020 and shows a consistent rise in passenger numbers from April, 2020 through at least July 2021.   From my own receiver's OpenSky upload data, which also shows the marked drop in uploaded messages between Sept 9-11, 2020,  it appears that there may also be a throttling of message uploads in place since September, 2020.  See the image below.  
Thanks in advance for any info,  Roger Rehr

Hi, and Thank You for your reply!

No, the prior receiver complaints were not in reference to my receiver and were not made by me.  My receiver continues to upload Mode-S messages, but "only" around 6 million per day instead of its previous 14 million or so. 

Your graphs on your Network Coverage and Facts page show that this was ( and is ) a system-wide phenomenon, not limited to just one or a few users.  I had originally included that graph in my original post, but your forum software limited me to one linked image so I chose the image of my own data instead.  Below is the graph from your Network Coverage and Facts page showing that you had a marked system-wide drop in collected mode-s reports that occurred between Sept 9 and Sept 11, 2020 which persists to this day:  

My original supposition was that you had initiated throttling of receiver mode-S reports on or around Sept 9, 2020 in order to improve your system performance and reduce your bandwidth and storage requirements.  If that is the case, I of course have no problem with your doing that.  Is that in fact what is happening here?  Old posts suggest that but do not state it explicitly.  I am uploading my data solely to support your system, so you don't need to change how you handle my data, I am just trying to understand the situation.

Thanks again for your response, and thanks in advance for further clarification!  
 

Thank you very much for the info and for OpenSky, which is a great resource for many (including me)! I do not need to download my S-mode data, so no need to activate my receiver. Thanks Again!!