John 17:12 (traditional text)
ημην μετ αυτων
αυτους εν τω
"While I was with them
in the world,
I was keeping
them in your name [Father]..."
INCLUDE LINE: A, CC3, DC, X, D, Δ Θ ψ 0141, f13, 33, 157, 579, Maj, f, q, Sy, arm, goth Byz, Maj (Majority of all continuous MSS)
OMIT LINE: P60(7th CE), P66, א, B, C*, D*, L, W, f1, 1071, pc, Lat, Co, Did
Another minor, but significant case of Haplography (homoioarcton - similar beginnings).
Its just a small stutter in the copying stream, but no argument can be made that anyone could even have conceived of adding "in the world" to this sentence, for any reason. The content of the phrase is so self-evident that no one could imagine needing to spell it out.
Only the original author (John the Evangelist), who is instead simply keeping a record of an actual speech, would have included this. You don't tug on superman's cape, and you don't needlessly shorten a speech from Jesus.
By now we've come to expect Aleph/B's ancestor to drop lines from time to time.
Why do all 'modern' versions leave out the text? Because the UBS-2 Greek text (following Westcott/Hort) has dropped the phrase, without any footnote at all. Most of the English translators were probably unaware of yet another undocumented and unwarranted alteration of the traditional text.