How to flush canvas before writing to file

[profhuster]

I have worked through the few example for ipycanvas. The show of the canvas in the notebook is prefect. I finally got the canvas to save to an image by putting
canvas.to_file("/Users/ME/Projects/myFig.png")
in a separate jupyter notebook cell. However usually only a partial image get written.
I have tried the callback function observing the trait save_to_file like
canvas.observe(save_to_file, "/Users/ME/Projects/myFig2.png")
without success.
I tried canvas.flush() without success.
I tried sleeping for 10 seconds - Nope.

I am running out of ideas.
Any advice?