I tested on:
wxPython 4.2.1 with Python 3.9 on a Mac, and it works.

However, with:
wxPython 4.2.1 with Python 3.10 on a Mac

I do see the failure.

So it's a 2.9 vs 3.10 issue, which is very odd.

It *could be an issue with a new numpy -- I"ll see about fixing the numpy warnings, and see if that helps.

Found it -- turns out wxPython used to simply truncate floats to int when you used them in a drawing call -- now it doesn't do that, and instead does mysterious things -- at least when using numpy arrays, which FloatCanvas makes heavy use of.

Anyway -- fixed in: #2448

However, I'm not sure when that might get merged -- I don't have permissions :-(

If you want to patch it yourself, you'll want the new FloatCanvas.py and DrawObjects.py