A download of several files is prepared in the background, and it is fixed to the versions that were there when you asked. Three things follow from that, and each of them surprises somebody.
You get a link when it is ready rather than a file straight away. A selection of forty documents takes a moment to gather, and a browser that waited for it would give up first.
Every file is checked again while the download is being built. A version that was withdrawn, revoked or is still being scanned in the meantime is left out, and the download tells you which ones and why.
The list inside the download says the same thing, so somebody who opens it in six months can see what was left out rather than assuming they have everything.
Check the count. A download that says "38 of 40" is telling you something.
The prepared download is deleted after a short time. That is not a fault: it is a copy of documents sitting outside the folders they are governed in, so it is not kept around.
Ask for it again if you need it. The new one is built from the versions that are current then, which may not be the same ones.
If somebody uploads a newer version of a document after you asked for the download, you get the one that was there when you asked. That is deliberate, so what you collected matches what you were looking at.
