A node closes its user connections as part of its transition to member state ROLLBACK. The ReshardingTest#stepUpNewPrimaryOnShard() method should swallow any network error when attempting to run the replSetStepUp command and move on to attempting to step up another secondary node.

const res = newPrimary.adminCommand({replSetStepUp: 1});
if (res.ok === 1) {
    replSet.awaitNodesAgreeOnPrimary();
    assert.eq(newPrimary, replSet.getPrimary());
    return;
}