**How to reproduce**
Clickhouse server 20.13.1.5273
```
CREATE TABLE default.test
(
`key` UInt32,
`ts` DateTime CODEC(DoubleDelta, LZ4),
`db_time` DateTime DEFAULT now() COMMENT 'spout-ignore' CODEC(DoubleDelta, LZ4)
)
ENGINE = MergeTree
PARTITION BY toStartOfTenMinutes(db_time)
ORDER BY (key, ts)
TTL db_time + toIntervalHour(3)
SETTINGS index_granularity = 8192, merge_with_ttl_timeout = 3600, min_rows_for_compact_part = 1000000, min_bytes_for_compact_part = 200000000, in_memory_parts_enable_wal = 0;


INSERT INTO test(key, ts) SELECT number % 1000, now() + intDiv(number,1000) FROM numbers(500);

SELECT * FROM test;
500 rows in set. Elapsed: 0.003 sec.

DETACH TABLE test;

ATTACH TABLE test;

SELECT * FROM test;

0 rows in set. Elapsed: 0.002 sec.
```

**Expected behavior**
Clickhouse would flush parts on disk.
{
    const auto settings = getSettings();
    if (parts_to_remove.size() > 1 && settings->max_part_removal_threads > 1 && parts_to_remove.size() > settings->concurrent_part_removal_threshold)
    {
        
        size_t num_threads = std::min<size_t>(settings->max_part_removal_threads, parts_to_remove.size());
        ThreadPool pool(num_threads);
        
        for (const DataPartPtr & part : parts_to_remove)
        {
            pool.scheduleOrThrowOnError([&, thread_group = CurrentThread::getGroup()]
            {
                SCOPE_EXIT_SAFE(
                    if (thread_group)
                        CurrentThread::detachQueryIfNotDetached();
                );
                if (thread_group)
                    CurrentThread::attachTo(thread_group);
                LOG_DEBUG(log, "Removing part from filesystem {}", part->name);
                part->remove();
            });
        }
        pool.wait();
    }