Users are added to site but do not show in site Users list

Hi all

I've just use Batch Create to add some existing network users to a network site. The users appear to be added to the site but in the site Users list they do not appear.

I can see all of the users that I have manually added, in our case it's teachers (9 of them) but I don't see any other users in the list. I haven't filtered the results in any way.
I can however see in the top right that the users must have been added because the user count is 48 users. (Attachment Batch Create 01)

If I go to the network dashboard and check out my registered users the users that I've added to the site show up there and show that they've been added to the site in the sites column. (Attachment Batch Create 02)

Interesting still, if I search in the specific site user list (where the users seem to be present but aren't showing up) I get a blank search result but saying 1 item. (Attachment Batch Create 03)

Perhaps this isn't a Batch Create issue? I've never seen this before. I've use BC to do the exact same thing many times before with normal results.