**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 task = std::make_shared<MergePlainMergeTreeTask>(*this, metadata_snapshot, false, Names{}, merge_entry, share_lock, common_assignee_trigger);
        assignee.scheduleMergeMutateTask(task);
        return true;
    }
    if (mutate_entry)
    {
        auto task = std::make_shared<MutatePlainMergeTreeTask>(*this, metadata_snapshot, mutate_entry, share_lock, common_assignee_trigger);
        assignee.scheduleMergeMutateTask(task);
        return true;
    }
    if (has_mutations)
    {
        
        
        std::lock_guard lock(mutation_wait_mutex);
        mutation_wait_event.notify_all();
    }
    bool scheduled = false;
    if (time_after_previous_cleanup_temporary_directories.compareAndRestartDeferred(
            getSettings()->merge_tree_clear_old_temporary_directories_interval_seconds))
    {
        assignee.scheduleCommonTask(ExecutableLambdaAdapter::create(
            [this, share_lock] ()
            {
                return clearOldTemporaryDirectories(merger_mutator, getSettings()->temporary_directories_lifetime.totalSeconds());
            }, common_assignee_trigger, getStorageID()),  false);
        scheduled = true;
    }
    if (auto lock = time_after_previous_cleanup_parts.compareAndRestartDeferred(