AssertionError and text placement parameters misunderstanding

Hi @ankush-me , I have this error and don't know what is incorrect? Is the AssertError important?

And can you explain what is this text placement parameters:

self.f_shrink = 0.90
self.max_shrink_trials = 5 # 0.9^5 ~= 0.6
self.p_flat = 0.10

because when I change it, nothing is changed with text on image