Just noticed the other day when using the stylus that the middle of the bottom half of the screen is unresponsive, if i use screen write and scribble lined horizontaly and verticaly there is about a centimetre area where no lines apear, get real anoyinh when your writing emails or texts as this is the area most used. just over 3 months old.
That's not good.
Assuming a soft reboot by turning it off and on does not help and the phone has not been dropped and the water sensors have not been tripped I would suggest visiting a Samsung Service Centre or Samsung Experience Store where they'll check it over under the 24 Month Manufacturing Warranty cover.
Current Phone ~ Samsung Note 9 Model: SM-N960 Duos 512Gb
Samsung Gear s3 Frontier Watch
As well as what @BandOfBrothers has said you can also try a quick hardware test on your phone:
If the screen is still unresponsive in parts then you can find your nearest Support Centre, HERE.
Just thought I'd share my experience with this issue. I had exactly the same problem with my Note 9, same dead spot... Turns out I have a magnet in my phone case, right beneath the dead spot, and taking my phone out of the case fixed the issue.
Hopefully this info helps anyone searching for this error in future!