i'm also facing the same problem and it's really annoying. This is my setup and how to easily reproduce. The key thing is that the images in note are Ratina capture 144dpi instead of regular 72dpi.
EN7.14 on MAC Mojave with macmini 2011 i7 CPU, 16G mem, 27" 2560x1440 monitor
if you capture 3 images using MACbook pro(ratina display) and put into one note and switched to macmini and try to scoll down this note, it'll be very very slow and lagging, the more ratina images(144dpi instead of 72 dpi) you put in one note, the more lagging you have.