Closing a single position
Every open position on the Trade Desk has its own Close button. It closes that one (account, contract) pair and leaves the rest of your book alone: the surgical alternative to Flatten all. A confirmation dialog always appears here, and it tells you exactly which of the two cases you are in.
In List view it is the Close at the end of the position's row; in Cards view, and on a phone, it sits at the top right of the position's card. It does the same thing everywhere. (If you hid the Close column from the list, switch it back on in the gear's column list.) Flatten all is not a single close: it closes every position on every account, the leader's included, and pauses copying until you press Resume copying.
Closing a leader position
Closing a position on the leader is just a leader trade. The dialog says so: "This sends a closing order on the leader account. Your followers close along with it, the same way they copy any other trade." The close fills on the leader, the fill mirrors out, and every follower exits with it, delta-exact. Copying stays on throughout.
Closing a follower position
Closing a position on a follower is different, and the difference is the part worth understanding. A closing order is sent for that position only, and copying for that instrument is paused on that account, in that group only.
It has to be. The follower's job is to match the leader. If you close a follower position while the leader still holds one, the next reconciliation pass would see the gap and re-open the position within seconds. So the close also pauses that account's rule in the group that copied the position, and the toast tells you plainly that copying that contract on that account "is paused so it is not re-opened. Turn it back on with the Follow switch."
When you want the account copying again, open that group's tab on the Trade Desk: the account's Follow switch there reads Off, and its Status column reads Paused in amber while copying runs (Off once the copier is stopped). Flip the switch On. The pause touches no other group: if the account also copies another leader in another group, it keeps copying there, and its switch on that tab stays On. The next reconcile then re-aligns the account with the leader, which can place catch-up orders at market within seconds.
If the close cannot complete
A close is an ordinary order, so it can miss: a dead session, a closed market. The copier retries the close on a re-sweep, checking every few seconds against the broker's actual book. If the position is still open after the retries, it raises a loud CLOSE FAILED event, a red toast that stays until you close it plus an entry in the Notifications panel, naming the contract and account and telling you to close it with your broker. It will not pretend the position is gone.
Quick answers
Why did copying stop on that account after I closed one position?
By design, and only for that instrument on that account, in the group that copied it. Without the pause, reconciliation would re-open the position you just closed. Re-enable it with the account's Follow switch on that group's tab, where the row now reads Off. Other groups the account copies in keep running.
Does closing a leader position pause anything?
No. Followers close along with it through the normal copy path, and copying continues.
The close failed. What now?
The copier keeps retrying, and if the position is still open after the retries you get a loud CLOSE FAILED alert, a red toast that stays until you close it, telling you to close it with your broker. Do that, then check the row matches before re-enabling anything.