This maybe just a palm/hand rejection glitch when moving your hand to write with the Pencil and somewhat typical of smart Bluetooth stylii that this can occur from time to time.
This is nothing serious or problematic. This can and does happen from time to time in any smart stylus supported drawing/writing app.
Notability seems to be one of these smart stylus supported apps that are more prone to stylus palm/hand rejection issues.
If you want to ensure more solid palm/hand rejection, you can always purchase a relatively inexpensive, special, non-electrical, lycra material based drawing tablet glove from online, from places like Amazon.
Do a search on Amazon for tablet drawing gloves.
These gloves come in a two or three finger variety and designed to cover the side of your hand and part of your palm for drawing on a tablet screen and the lycra based material acts as an electrical isolator, isolating your body’s electrical current in your hand.
These can be purchased seperately or in packs of different amounts and come in small, medium and large hand sizes, in some cases.
I use one of these on my iPad all the time to draw/write on my iPad to make sure I get more total hand/palm coverage/isolation for best palm rejection in a tablet app designed for stylii that support palm rejection.