Is my coding for my kalman filter off when testing this specific set of pairs?

Question

My kalman filter seems to be off for this specific set of pairs I'm looking at. As you can see, in the kalman filtered linear regression, there seems to be an outlying blue line nowhere near the data on the scatter plot. Did I do something wrong? How do I fix it so the Kalman filtered linear regression lines and kalman filtered spread to better match the scatter plot and spread time series?Here's the code