I think I discovered the issue. Some of the USPS tracking number have spaces in them, and those are not marked as delivered, although they have been delivered. Is there a way to make the plugin remove white spaces in the middle of the tracking number? One of the USPS tracking numbers is: 9405 5036 9930 0000 .....
Another one without spaces is marked as delivered.
However, I think the Scheduled Task runs every day, but doesn't check the UPS tracking numbers. I'll get back to you. I have 2 UPS packages scheduled to be delivered by Friday. I will check and see if the plugin automatically marks them as delivered.
Thank you for your support!