You are a Machine Learning Engineer working on an image segmentation model for a self-driving car application. After deploying the first version of the model, you observe a significant decline in the area under the curve (AUC) metric. Upon further investigation through video recordings, you notice that the model's performance is suboptimal in scenarios with highly congested traffic, whereas it performs as expected in less congested conditions. Considering the need for the model to perform reliably across all traffic conditions to ensure safety and compliance with regulatory standards, what is the most probable cause for this outcome? Choose the best option.