You have to provide the following information whenever possible.

**Describe the bug**
This query fails with the latest stable version 21.5.5.12. It worked with the last stable version 21.4.7.3.

**Does it reproduce on recent release?**
yes

**How to reproduce**
21.5.5.12

```
SELECT
    label,
    number
FROM
(
    SELECT
        'a' AS label,
        number
    FROM
    (
        SELECT number
        FROM numbers(10)
    )
    UNION ALL
    SELECT
        'b' AS label,
        number
    FROM
    (
        SELECT number
        FROM numbers(10)
    )
)
WHERE number IN
(
    SELECT number
    FROM numbers(5)
)
```

**Expected behavior**
Query should run without errors

**Error message and/or stacktrace**
```
Received exception from server (version 21.5.5):
Code: 49. DB::Exception: Received from localhost:9000. DB::Exception: Block structure mismatch in Pipe::unitePipes stream: different names of columns:
label String String(size = 0), number UInt64 UInt64(size = 0), 'b' String Const(size = 0, String(size = 1))
label String String(size = 0), number UInt64 UInt64(size = 0), 'a' String Const(size = 0, String(size = 1)).
```

if (visited_nodes.count(child) == 0)
            {
                visited_nodes.insert(child);
                stack.push({.node = child, .is_predicate = is_conjunction});
                break;
            }
            if (allowed_nodes.contains(child))
                ++cur.num_allowed_children;
            ++cur.next_child_to_visit;
        }
        if (cur.next_child_to_visit == cur.node->children.size())
        {
            if (cur.num_allowed_children == cur.node->children.size())
            {
                if (cur.node->type != ActionsDAG::ActionType::ARRAY_JOIN && cur.node->type != ActionsDAG::ActionType::INPUT)
                    allowed_nodes.emplace(cur.node);
            }
            else if (is_conjunction)
            {
                for (const auto * child : cur.node->children)
                {
                    if (allowed_nodes.count(child))
                    {
                        if (allowed.insert(child).second)
                            conjunction.allowed.push_back(child);
                    }
                }
            }
            else if (cur.is_predicate)
            {