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)).
```

for (const auto * output : index)
        {
            if (node_to_column.count(output) == 0)
            {
                std::stack<Frame> stack;
                stack.push({.node = output});
                while (!stack.empty())
                {
                    auto & frame = stack.top();
                    const auto * node = frame.node;
                    while (frame.next_child < node->children.size())
                    {
                        const auto * child = node->children[frame.next_child];
                        if (node_to_column.count(child) == 0)
                        {
                            stack.push({.node = child});
                            break;
                        }
                        ++frame.next_child;
                    }
                    if (frame.next_child < node->children.size())
                        continue;
                    stack.pop();
                    ColumnsWithTypeAndName arguments(node->children.size());
                    for (size_t i = 0; i < arguments.size(); ++i)
                    {
                        arguments[i] = node_to_column[node->children[i]];
                        if (!arguments[i].column)
                            throw Exception(ErrorCodes::NOT_FOUND_COLUMN_IN_BLOCK,
                                            "Not found column {} in block", node->children[i]->result_name);