I think I've found the culprit.
I downloaded the movie to check in Quicktime, thus eliminating any playback errors from youtube. Looked normal to me, but just to make sure I imported the clip into TVPaint and marked the same spot in some consecutive frames:
As you can see, the image advances the exact same amount in every frame, so AS did its job perfectly.
What you should notice as well is that the pink doorframe is of exactly the same width as the pan increment! And the vertical lines of the cars are the same or even smaller. What happens is that such a small line will blink. It's there in one position in only one frame, then vanished in the next. There is no overlap. You created a perfect example of "shatter".
What can you do about it? Change the pan speed, or change the artwork. You need to create overlap of at least the brightest elements, or make increments large enough that shatter doesn't happen.
In general, any pan artwork should avoid too many vertical lines. The corners of a house are OK, the picket fence is not. To reduce shatter, reduce contrast in BG elements.
If you can't change the artwork, change the pan. Make it so fast that it moves half a car's length between frames. Or make it so slow that it moves less than half a line width between frames. Experiment with settings: avoid linear interpolation, use a slow out, or combine pan and zoom in one movement - anything which will change the increments over time.
If you're not going to expose your movie on film stock, don't use 24 FPS. Use 25 or 30 FPS, as by the requirements of your broadcaster, and thus avoid further deterioration from frame rate conversion.
