I am a paying customer who has been suffering with this issue for several years. I am a software engineer and I use EN to track my daily work. I like to select text, change font, colors, etc. It is how I think. The notes slow down after abut two weeks worth of daily note taking. I have been thru two new macbooks, with the same exact results. A few years ago I even had a case open and they could see with me where it was hogging CPU. They told me at the time that they could not support notes greater than a certain size (I think it was 30K characters) and basically closed the case.
I am starting to look for a different product and will cancel my subscription.