I did a test download using monthly averages with the full sensor list. Upon a quick eyeball, I’d say around 90% of the sensors in the list have data from the time period you’re looking at. The issue you’re running into must be an issue with the code.
Another option would be to use the PurpleAir Data Download Tool. This tool will give you an easy interface for downloading historical data. You can even turn the sensor list you shared into a CSV and then upload that CSV into the Download Tool to autofill the “sensor index” field with all of the sensors, which will make things much easier. I can offer more detailed instructions on that process if you’re curious.