This began in v3.9 and continues in v4.0
It is so heavily using the CPU that the mac heats up and runs its fans full speed.

• It lags in mouse clicks versus mouse position; it does register the button click, but only after a delay of about 1 second. Likewise, the button release is delayed. Meanwhile, the mouse cursor on screen is behaving normally (no lag). This results in drag-select really screwing up, and in dragging objects getting missed and/or dropped in the wrong place.
• Typing a text item, I can see the screen fall behind - sometimes by up to several seconds - and then catch up as I wait, jaw dropped.
• Modifier keys (Command, Shift, etc) are often ignored. Cmd-P (for print), for example, thinks I'm pressing only "p".
• Even when totally idle for many minutes, the CPU is running hot. It drops back down as soon as I quit MyDraw.

The above occurs regardless whether I have the external monitor connected or not.
This may be a particular drawing that I'm making. I created it 100% in MyDraw (v3.9), and it is 133KB in size (is that large? the drawing doesn't seem super-complex).

MyDraw 4.0.0 build date 7/16/2019
macOS 10.14.5 on MacBookPro mid-2015