I do find it a bit trickier sometimes than the SP2. I did find on suggestion from someone on the forum to use full screen for modern OneNote and that cured my problems. I'm left handed and if you have more than one page open the palm rejection doesn't work until the pen engages the page. The palm rejection on the SP2 actually works better as it is built into the screen whereas on this, it seems to be activated by proximity of the pen.
I think also accidently touching one of the two buttons can cause issues also.