Hi,
I've noticed that when using the sketch function in a note, the pen tool stops responding after a number of strokes in MacOS Evernote (10.2.4) when using a Wacom Intuos Medium tablet (Driver Version 6.3.40-2) in macOS Catalina 10.15.7 .
Saving the sketch by clicking on "Done" saves the drawing as one would expect, and returning to the main body of the note and clicking on "Edit and Sketch" at the top of the sketch allows continued editing of the same sketch until the same problem reoccurs.
Thankfully no data is lost - but the continual starting and stopping is rather distracting when brainstorming in sketch mode.