[system test] found mutation_queue_size stat having negative value (-2540)

'HISTORY:o3_result_rating:timings/storage_snapshot_create': '0 0 0',

'CUSTOMER:#primary:timings/storage_meta_set': '0 0 0',

'HISTORY:o3_result_rating:insert_bytes': 43409408,

'default:default_result_ratings_claims_pindex (replica 1):avg_scan_request_alloc_latency': 6126,

'default:default_result_ratings_claims_pindex:recs_on_disk': 0,

'DISTRICT:o2_result_rating:scan_cache_hit_aggr': 0,

'default:mutation_queue_size': -2140,

'DISTRICT:o2_result_rating:num_requests_aggr': 81,

'17656998409915857210:completion_progress': 4636737291354636288,

'default:default_result_ratings_claims_pindex (replica 1):avg_drain_rate': 1727,

'default:default_result (replica 1):timings/storage_snapshot_close': '0 0 0',

'default:default_result_ratings_claims_pindex (replica 1):build_progress': 100,

'default:default_result_ratings_claims_pindex:timings/storage_meta_get': '0 0 0',

'default:default_result_ratings_claims_pindex:flush_queue_size': 0,

'default:default_result_ratings_claims_pindex (replica 1):num_rows_returned': 0,

'CUSTOMER:#primary:timings/storage_iterator_next': '0 0 0',

'CUSTOMER:#primary:timings/storage_get': '0 0 0',