An engineer trains a sequence processing model on a dataset where the longest text is 512 tokens. The model performs well on texts up to this length. However, when tested on a 1000-token document, the model's output becomes incoherent for the latter half of the text. A visualization of the numerical signals used to represent token positions shows a clear, repeating pattern for the first 512 positions, but a chaotic, noisy pattern for all positions thereafter. What is the most likely explanation for this specific failure mode?

Diagnosing Model Failure on Long Sequences

Visual Example of Positional Encoding Failure

Explaining Positional Encoding Failure