Do you have the note 8 in a case that has a magnetic closure? I did, and it caused issues with the stylus working irratically and sometimes becoming unresponsive. Removed the case and all works fine.
Mine was doing this same thing. My wife's was not so I figured it was my phone. I did a factory data reset and that didn't fix it. Went to Verizon on the 15th to trade it out and.......New one was doing this same thing. Turns out there's a problem if you have triple tap on (where you tap the screen 3 times to zoom in) and try to use the pen. I turned that off and it works great now. I haven't called Samsung yet to inform them of this problem.
Thank you so much for your post! My problem with the phone freezing every time I tried to use the S-pen was solved with your suggestion.
For those who have not read his/her post, all you have to do is turn off magnification gestures. (Settings > Accessibility > Vision > Magnification gestures)
At least it worked for me! Thanks again!