In your comments which are correct the painted engine glow sans star destroyer to accompany it was removed.
But actually that was a missing star destroyer element. The engine glow was done but the star destroyer got missed in the original film.
Bit of trivia there.
But the Special Edition did not do “the right” thing
THere are meant to be 5 star destroyers and the Executor. One of the Star destroyers is hidden behind the Executor we see it drop down a few shots earlier.