Lane lines jittery for P2

[marc88]

It seems that you implemented the sliding window search in function find_lane_pixels, and it is called from fit_polynomial, but the function fit_polynomial is not called from the main pipeline (the call is commented out). This means that you use the proximity-search always. But for the proximity search you already have to have a good line candidate (left_fit & right_fit). Actually these variables are not set in the main pipeline, you use some fixed values from an earlier cell of the notebook. Most probably that is the reason why the pipeline does not work at the beginning when the road is curving left: the upper end of the road (on the birds-eye view image) is not within the range of those fixed lines.
Here I suggest using the sliding window algorithm first, and if you have a reliable lane lines (polynomials) you can use the proximity search