### Discussed in https://github.com/apache/airflow/discussions/19366

<div type='discussions-op-text'>

<sup>Originally posted by **a-pertsev** November  2, 2021</sup>
### Apache Airflow version

2.2.1 (latest released)

### Operating System

Ubuntu 20.04 LTS

### Versions of Apache Airflow Providers

apache-airflow-providers-amazon==2.3.0
apache-airflow-providers-apache-cassandra==2.1.0
apache-airflow-providers-ftp==2.0.1
apache-airflow-providers-google==6.0.0
apache-airflow-providers-http==2.0.1
apache-airflow-providers-imap==2.0.1
apache-airflow-providers-jdbc==2.0.1
apache-airflow-providers-mysql==2.1.1
apache-airflow-providers-postgres==2.3.0
apache-airflow-providers-presto==2.0.1
apache-airflow-providers-slack==4.1.0
apache-airflow-providers-sqlite==2.0.1

### Deployment

Virtualenv installation

### Deployment details

_No response_

### What happened

Got error when manually run newly created task in already finished dag run (in UI).

### What you expected to happen

"Run" button should work without exceptions.

### How to reproduce

1. Define a dag with some tasks.
2. Create dag run (manually or by schedule)
3. Add new task into dag, deploy code
4. Select new task in UI and press "Run" button

### Anything else

_No response_

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)
</div>
airflow/www/views.py
nonlocal node_count
            node_count += 1
            visited.add(task)
            task_id = task.task_id
            node = {
                'name': task.task_id,
                'instances': [encode_ti(task_instances.get((task_id, d))) for d in dates],
                'num_dep': len(task.downstream_list),
                'operator': task.task_type,
                'retries': task.retries,
                'owner': task.owner,
                'ui_color': task.ui_color,
            }
            if task.downstream_list:
                children = [
                    recurse_nodes(t, visited)
                    for t in task.downstream_list
                    if node_count < node_limit or t not in visited
                ]
                
                
                
                if task.task_id not in expanded:
                    children_key = 'children'
                    expanded.add(task.task_id)
                else:
                    children_key = "_children"