To rephrase my question more in line with the OP
**What is it that makes kneeling during the *Agnus Dei ***a traditional practice?
That is: Is it a traditional practice? I confess, it has been long enough since I have been to a TLM that I know not the rubrics, but I find this
crib sheet from *Una Voce *America, which indicates kneeling from the *Sanctus *until Communion. Why would someone of traditional mind kneel during the *Agnus Dei *but not, say, during the
Pater Noster?
In my experience, I have never noticed anyone attending a Mass according to the current Missal to kneel during the *Agnus Dei *nor do I know of any parishes/dioceses where this is the practice?

tee