PurpleAir sensors stopped reporting data to ThingSpeak on October 25. Because of this, any data after that date will not appear in the Sensor Data Download Tool.
We are working on updating the online download tool. Once updated, you will be able to download data from any time period again.
The PurpleAir API at api.purpleair.com will provide historical data. More information on accessing the historical endpoints is available here: Historical API Endpoints are now Restricted.
12-29-2022 Edit: Graph data can now be downloaded from the PurpleAir map. More information is available here: Download Map Graph Data.