I came across this in Mishna B'rura 581:27:
ואין לילך על קבר אחד ב״פ ביום אחד.
That is, roughly:
And one should not go to one grave twice in one day.
(This is in Baer Hetev :17 also, who cites the Arizal as a source.) Why not?
(I translate it as "go to" not "walk on" in light of MB 539:41, who in that way interprets the same phrase in Rama there, and who says not to walk on a grave altogether.)
Daily Halacha brings this in the name of Rabbi Yehuda HaChasid and says that this restriction is Kabalistic.
Nitei Gavriel - Aveilus2 88:1:1 mentions this in the name of Magein Avraham 581:16 quoting the Arizal, Rabbi Yehuda HaChasid 12, Shela, Elya Raba 224:7, Rabbi Akiva Eiger 376 and others. In note 2 he brings a possible reason from Damesek Eliezer. That by returning the same day you are showing that the departed did not intercede on your behalf and it is a shame for the departed to do so.
