In the Biblia Hebraica Stuttgartensia (page 25 print) Genesis 18:22 is notated with two lowercase 'a's one before (and Avraham) ‬וְאַ֨בְרָהָ֔ם and one attached to יְהוָֽה (YHWH )

a‬וְאַ֨בְרָהָ֔ם עֹודֶ֥נּוּ עֹמֵ֖ד לִפְנֵ֥י יְהוָֽהa‬

but, Avraham still stood before YHWH (Genesis 18:22)

That directs us to the apparatus or footnotes:

22 a–a Tiq soph, lect orig אברהם … ויהוה

'Tiq soph' tells us that we are encountering what is know as a Tiqqūn sōferīm

'lect' is short for 'lectio' (reading)

'Orig' is short for originalis (original)

What, the abbreviated notes from the BHS' textual apparatus are telling us is that originally the text may have 'theoretically' read:"but, YHWH still stood before Avraham". This text is one of the 18 tiqqūnēy sōferīm texts that were alleged (according to tradition) changed by the ancient scribes for theological reasons. This begs the question: "what was the theological reason that the text was supposedly changed for"? Some claim that this text put YHWH is less role by having YHWH stand before Avraham rather than the other around, but it, in my opinion, is more likely that the alleged Scribes were worried if read that way it would paint an anthropomorphic picture of YHWH by directly stating that YHWH was actually standing in front of Avraham. The Masoretes themselves did not make the Tiqquney Soferim changes but only noted changes they believed had happened. However, Masoretes were Karaite Jews rather than Rabbinic Jews and they would have outright rejected Midrashic/oral interpretations that claimed that YHWH would either manifest himself personally as the Memra and or Metatron or that they were his mediator or conduit with which to speak to mankind. I have no doubt that would not have also have found John 8:56-58 problematic none the less they wanted to make sure that any changes or textual phenomenon were noted.

Sources Cited:
(1) Biblia Hebraica Stuttgartensia: SESB Version. electronic ed. Stuttgart: German Bible Society, 2003. Print.
(2) Weil, Gérard E., K. Elliger, and W. Rudolph, Deutsche Bibelgesellschaft. Biblia Hebraica Stuttgartensia. 5. Aufl., rev. Stuttgart: Deutsche Bibelgesellschaft, 1997. Print.