The elevators are probably causing rapid blind spots (shadows) while the user is moving around, 802.11k is indeed useful in this case for cutting down scan time, since iOS will still scan with filtered channels.

It's an interesting setup, looking forward to an update.

You're not getting it. The lift shafts are lined, this is an armored concrete building in Europe.

The post to which you're replying is implying that the lift shafts are entirely opaque to the wireless signal.

So it's fine if the user doesn't have a shaft between them and the AP. When they move so a straight line from the device to the AP crosses through a lift shaft, they enter the wireless "shadow" cast by that shaft, preventing them from contacting the AP. When they take another step forward the device might "come out of the shadow".

This is a difficult situation to deal with in roaming, where the visible AP set changes rapidly as the user moves a small amount.

TL;DR: I'm pretty sure the parent you're replying to "got it" and you didn't understand what they were trying to say.