**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.
{
    auto lock = lockParts();
    Int64 max_block_num = 0;
    for (const DataPartPtr & part : data_parts_by_info)
        max_block_num = std::max({max_block_num, part->info.max_block, part->info.mutation});
    return max_block_num;
}
void MergeTreeData::loadDataPartsFromDisk(
    DataPartsVector & broken_parts_to_detach,
    DataPartsVector & duplicate_parts_to_remove,
    ThreadPool & pool,
    size_t num_parts,
    std::queue<std::vector<std::pair<String, DiskPtr>>> & parts_queue,
    bool skip_sanity_checks,
    const MergeTreeSettingsPtr & settings)
{
    
    pool.setMaxThreads(std::min(size_t(settings->max_part_loading_threads), num_parts));
    size_t num_threads = pool.getMaxThreads();
    std::vector<size_t> parts_per_thread(num_threads, num_parts / num_threads);
    for (size_t i = 0ul; i < num_parts % num_threads; ++i)
        ++parts_per_thread[i];
    
    
    std::vector<std::vector<std::pair<String, DiskPtr>>> threads_parts(num_threads);
    std::set<size_t> remaining_thread_parts;