Quoting George Martin: "There is the end section of the orchestrated version of the song, where the rhythm is too loose to use. In spite of all our editing, I just could not get a unified take with complete synchronicity throughout. The obvious answer would have been to fade out the take before the beat goes haywire. But that would have meant discarding one of my favourite bits, which included some great trumpet and guitar playing, as well as the magical random mellotronic note-waterfall John had come up with. It was a section brimming with energy, and I was determined to keep it. We did the only thing possible - we faded the song right out just before the point where the rhythm goes to pieces, so the listener would think it was all over, then gradually faded it back up again, bringing back our glorious finale” (Martin, page 23-24).
That is why the final edit of "Strawberry Fields Forever" fades out, then fades back in, before fading out once more.
That original recording (with its “too loose to use” rhythm), may be found in this YouTube video at 6:40.
Martin, George with William Pearson. With a Little Help from My Friends: The Making of Sgt. Pepper. Little Brown and Company, Boston, MA, 1994.