FOUND THE SOLUTION!!! I have been trying to update my T-Mobile Samsung Galaxy S9 to the new software for the last 8 months with no luck. Kept getting stuck at 28% every time. Tried everything including what was mentioned on this website.
Called samsung and they did troubleshooting, had me reset my phone settings (not factory reset), that didn't work. They said the only solution was to reset the phone to factory settings and start over again. I did NOT want to do this but knew it had to be done so I can update to latest version.
I downloaded the DESKTOP version of Smart Switch. https://www.samsung.com/us/support/owners/app/smart-switch
When you install this software on your computer and connect your phone via cable, there is an option that says UPDATE PHONE SOFTWARE. I was like, why not, lets give it a try. IT WORKED!
I know have the latest version of the software because I did the full install through the Smart Switch software.
Hopefully this will help you all out as I know how frusturating this is. I believe the error is being caused from a glitch in the download which is why connecting to your computer downloads a much cleaner version from high speed internet.
This should work for any phones having similar programs of getting stuck in upgrading loop.
I tried that and it tells me my current version, CSAA, is the latest and up to date. Check for updates says that too... but AT&T's website says N960USQS1CSE1 is the latest version.
Buying this Note9 has been the worst choice ever, nothing but problems with this garbage and no real useful answers from Samsung or AT&T.
I am having the same problem - my samsung galaxy S9 is not receiving the latest updates. I tried clearing the cache, resetting the software settings - but nothing. Is there anything else i can do?
Have you tried using Smart switch the pc version to update the device?