**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 StorageMetadataPtr & metadata_snapshot,
    bool aggressive,
    const String & partition_id,
    bool final,
    String * out_disable_reason,
    TableLockHolder & ,
    std::unique_lock<std::mutex> & lock,
    bool optimize_skip_merged_partitions,
    SelectPartsDecision * select_decision_out)
{
    auto data_settings = getSettings();
    auto future_part = std::make_shared<FutureMergedMutatedPart>();
    if (storage_settings.get()->assign_part_uuids)
        future_part->uuid = UUIDHelpers::generateV4();
    
    CurrentlyMergingPartsTaggerPtr merging_tagger;
    MergeList::EntryPtr merge_entry;
    auto can_merge = [this, &lock](const DataPartPtr & left, const DataPartPtr & right, String *) -> bool
    {
        
        
        if (!left)