I want to create some aggregations of table. But when I look at execution plan I find out that there is massive row increase in sort (from 5 121 to 1 453 235 569). Why this is happend? What can cause this increase?

More info:
Original table has this schema:

CREATE TABLE event (
    deviceid varchar NOT NULL,
    "time" timestamptz NOT NULL,
    signal_quality float8 NULL,
    packet_loss float8 NULL,
    ping float8 NULL,
    jitter float8 NULL,
    download float8 NULL,
    upload float8 NULL,
    latency float8 NULL,
    profinet float8 NULL
);

Next table has data about start tests:

CREATE TABLE start_test (
    deviceid varchar NOT NULL,
    "time" timestamptz NOT NULL
);

I want to agregate data for each test. For one test there will be more rows, each row contains one type of aggregation – for example one row for minimum, one row for median,…
Here is subset of aggregation script:

WITH event_cycle AS (
    SELECT 
        e.*, 
        sc.time as start_time, 
        sc.end_time as end_time
    FROM (
        SELECT 
            *
        FROM event
    ) e 
    LEFT JOIN (
        SELECT *, COALESCE(LEAD(time) OVER(PARTITION BY deviceid ORDER BY time), NOW()) as end_time
        FROM start_test
    ) sc ON sc.time <= e.time AND e.time < sc.end_time AND e.deviceid = sc.deviceid
), bounds AS (
    SELECT 
        start_time start_time_b, 
        min(end_time) end_time_b,
        deviceid deviceid_b, 
        --low
        PERCENTILE_DISC(0.005) WITHIN GROUP(ORDER BY signal_quality) as signal_quality_low,
        --high
        PERCENTILE_DISC(0.995) WITHIN GROUP(ORDER BY signal_quality) as signal_quality_high
    FROM event_cycle
    GROUP BY start_time, deviceid
), data_with_boundaries AS (
    SELECT *
    FROM event_cycle ec
    LEFT JOIN bounds b ON b.start_time_b <= ec.time AND ec.time < b.end_time_b AND ec.deviceid = b.deviceid_b
)
SELECT *
FROM (
  SELECT 
      min(time) as start_time, 
      max(time) as end_time,
      deviceid, 
      'min' as agg_type,
      min(signal_quality) as signal_quality
  FROM event_cycle
  GROUP BY start_time, deviceid
) min
UNION ALL
SELECT *
FROM (
  SELECT 
      min(time) as start_time, 
      max(time) as end_time,
      deviceid, 
      'median' as agg_type,
      PERCENTILE_DISC(0.5) WITHIN GROUP(ORDER BY signal_quality) as signal_quality
  FROM event_cycle
  GROUP BY start_time, deviceid
) median
UNION ALL
SELECT *
FROM (
  SELECT 
      min(time) as start_time, 
      max(time) as end_time,
      deviceid, 
      'ipr_avg' as agg_type,
      avg(CASE WHEN signal_quality 
                        BETWEEN signal_quality_low
                        AND signal_quality_high
                  THEN signal_quality 
              ELSE NULL 
          END) as signal_quality
  FROM data_with_boundaries
  GROUP BY start_time, deviceid
) ipr_avg

This is whole query plan:

Append  (cost=65349092.63..2218756400.84 rows=120000 width=88) (actual time=108568.862..305159.053 rows=15363 loops=1)
  CTE event_cycle
    ->  Hash Left Join  (cost=652.57..23608823.05 rows=161244967 width=99) (actual time=11.336..107377.365 rows=855037 loops=1)
          Hash Cond: ((event.deviceid)::text = (sc.deviceid)::text)
          Join Filter: ((sc."time" <= event."time") AND (event."time" < sc.end_time))
          Rows Removed by Join Filter: 1451937372
          ->  Seq Scan on event  (cost=0.00..17802.37 rows=855037 width=83) (actual time=0.095..338.366 rows=855037 loops=1)
          ->  Hash  (cost=588.92..588.92 rows=5092 width=27) (actual time=11.190..11.193 rows=5118 loops=1)
                Buckets: 8192  Batches: 1  Memory Usage: 359kB
                ->  Subquery Scan on sc  (cost=423.43..588.92 rows=5092 width=27) (actual time=8.076..10.517 rows=5118 loops=1)
                      ->  WindowAgg  (cost=423.43..538.00 rows=5092 width=27) (actual time=8.075..10.152 rows=5118 loops=1)
                            ->  Sort  (cost=423.43..436.16 rows=5092 width=19) (actual time=8.060..8.260 rows=5118 loops=1)
                                  Sort Key: start_test.deviceid, start_test."time"
                                  Sort Method: quicksort  Memory: 592kB
                                  ->  Seq Scan on start_test  (cost=0.00..109.92 rows=5092 width=19) (actual time=0.017..0.557 rows=5118 loops=1)
  ->  Subquery Scan on min  (cost=41740269.58..44159744.08 rows=40000 width=88) (actual time=108568.860..108914.711 rows=5121 loops=1)
        ->  GroupAggregate  (cost=41740269.58..44159344.08 rows=40000 width=96) (actual time=108568.860..108914.282 rows=5121 loops=1)
              Group Key: event_cycle.start_time, event_cycle.deviceid
              ->  Sort  (cost=41740269.58..42143382.00 rows=161244967 width=56) (actual time=108568.845..108751.590 rows=855037 loops=1)
                    Sort Key: event_cycle.start_time, event_cycle.deviceid
                    Sort Method: external merge  Disk: 38608kB
                    ->  CTE Scan on event_cycle  (cost=0.00..3224899.34 rows=161244967 width=56) (actual time=11.338..108096.087 rows=855037 loops=1)
  ->  Subquery Scan on median  (cost=41740269.58..44159844.08 rows=40000 width=88) (actual time=812.829..1215.500 rows=5121 loops=1)
        ->  GroupAggregate  (cost=41740269.58..44159444.08 rows=40000 width=96) (actual time=812.828..1214.812 rows=5121 loops=1)
              Group Key: event_cycle_1.start_time, event_cycle_1.deviceid
              ->  Sort  (cost=41740269.58..42143382.00 rows=161244967 width=56) (actual time=812.797..1009.458 rows=855037 loops=1)
                    Sort Key: event_cycle_1.start_time, event_cycle_1.deviceid
                    Sort Method: external merge  Disk: 38608kB
                    ->  CTE Scan on event_cycle event_cycle_1  (cost=0.00..3224899.34 rows=161244967 width=56) (actual time=0.058..229.673 rows=855037 loops=1)
  ->  Subquery Scan on ipr_avg  (cost=2035162059.84..2106827389.62 rows=40000 width=88) (actual time=194608.278..195027.597 rows=5121 loops=1)
        ->  GroupAggregate  (cost=2035162059.84..2106826989.62 rows=40000 width=96) (actual time=194608.276..195027.074 rows=5121 loops=1)
              Group Key: ec.start_time, ec.deviceid
              ->  Sort  (cost=2035162059.84..2044120113.56 rows=3583221489 width=72) (actual time=194608.252..194833.440 rows=855037 loops=1)
                    Sort Key: ec.start_time, ec.deviceid
                    Sort Method: external merge  Disk: 45552kB
                    ->  Merge Left Join  (cost=85903271.20..731689364.04 rows=3583221489 width=72) (actual time=1673.883..194023.850 rows=855037 loops=1)
                          Merge Cond: ((ec.deviceid)::text = (b.deviceid_b)::text)
                          Join Filter: ((b.start_time_b <= ec."time") AND (ec."time" < b.end_time_b))
                          Rows Removed by Join Filter: 1452792384
                          ->  Sort  (cost=41740269.58..42143382.00 rows=161244967 width=56) (actual time=739.639..1020.075 rows=855037 loops=1)
                                Sort Key: ec.deviceid
                                Sort Method: external merge  Disk: 38608kB
                                ->  CTE Scan on event_cycle ec  (cost=0.00..3224899.34 rows=161244967 width=56) (actual time=0.027..182.877 rows=855037 loops=1)
                          ->  Sort  (cost=44163001.63..44163101.63 rows=40000 width=64) (actual time=934.232..51961.852 rows=1453235569 loops=1)
                                Sort Key: b.deviceid_b
                                Sort Method: quicksort  Memory: 593kB
                                ->  Subquery Scan on b  (cost=41740269.58..44159944.08 rows=40000 width=64) (actual time=638.853..932.024 rows=5121 loops=1)
                                      ->  GroupAggregate  (cost=41740269.58..44159544.08 rows=40000 width=64) (actual time=638.852..931.538 rows=5121 loops=1)
                                            Group Key: event_cycle_2.start_time, event_cycle_2.deviceid
                                            ->  Sort  (cost=41740269.58..42143382.00 rows=161244967 width=56) (actual time=638.826..788.470 rows=855037 loops=1)
                                                  Sort Key: event_cycle_2.start_time, event_cycle_2.deviceid
                                                  Sort Method: external merge  Disk: 35424kB
                                                  ->  CTE Scan on event_cycle event_cycle_2  (cost=0.00..3224899.34 rows=161244967 width=56) (actual time=0.027..184.881 rows=855037 loops=1)
Planning Time: 0.638 ms
Execution Time: 305182.448 ms