How did the Stupefied Yaxley manage to get up to the Ministry lobby so quickly?

Question

In The Deathly Hallows, Harry hits Yaxley with a Stunning Spell in the Ministry of Magic.

Yaxley, confused, looked around for the source of the trouble and saw Harry's disembodied hand and wand pointing at him. He tried to draw his own wand, but too late.
"Stupefy!"
Yaxley slid to the ground to lie curled on the floor.
_{(Deathly Hallows, Chapter 13, The Muggle-Born Registration Commission).}

Now being Stupefied means you're out for the count. Unless somebody else performs Renervate on you then you'll remain unconscious for a while, as Pottermore confirms:

The effects of the Stunning Spell may be counteracted by 'Rennervate', but will also wear off with time on their own.

Yaxley, Umbridge, Harry, Hermione and Mrs Cattermole were the only people in the chamber at that moment in time. The latter three were escaping and the former two were both Stunned. Yet, moments later, Yaxley appears up in the foyer to cut off Harry, Ron and Hermione's escape.

Yaxley had burst out of another lift and was running towards the group beside the fireplaces into which all of the Muggle-borns but Mrs Cattermole had now vanished.
_{(Deathly Hallows, Chapter 13, The Muggle-Born Registration Commission).}

If Yaxley was Stupefied, how did he manage to get up to the foyer so quickly? With the facts as we know them, shouldn't his appearance have been impossible?

Answer 1

Here's a quote from later in the chapter:

When the Patronuses glided out of the dungeon there were cries of shock from the people waiting outside. Harry looked around; the dementors were falling back on both sides of them, melding into the darkness, scattering before the silver creatures.

And later, when Ron finds Harry, he says this:

“Harry, they know there are intruders inside the Ministry, something about a hole in Umbridge’s office door, I reckon we’ve got five minutes if that —”

It would be easy for anyone involved in the Ministry to track the intruders to the courtroom when they found the bodies of Mafalda and Runcorn (the real ones) and/or followed the word of disturbances. There they would find Umbridge and Yaxley and, presumably, Renervate them. Given that Harry was leading a rather large number of people, and Yaxley was not, it would be easy for Yaxley to catch up to him.

And that's assuming those were the only five in the room. Though it never says there are others, it never says there aren't either. Someone in the courtroom might have done it.