I have found that when creating multiple items on a canvas that in order for them to be drawn as they're created on Windows I have to use 'update' whereas on Linux I can use 'update idletasks'.
I have see this behaviour in both the latest 8.5 and 8.6 from AS. The attached file should draw some coloured random koch snowflakes as they're created - I've annotated the problem area. The file itself will run ok since there is a platform dependent selection of the update mode.
Code that can be used to demonstrate the problem with 'update idletasks' on windows