Postgres - Update Performance degraded - postgresql

Question

Can someone please help assist in identifying why below statement which used to take 2 hours is not taking 6 hours without volume increase being a factor.
with P as
(SELECT DISTINCT CD.CASE_DETAIL_ID, SVL.SERVICE_LEVEL_ID\n
FROM report_fct CD LEFT JOIN SERVICE_LEVEL SVL ON SVL.ORDER_TYPE_CD = CD.ORDER_TYPE_CD\n
AND SVL.SOURCE_ID = CD.SOURCE_ID\n AND SVL.AREA_ID = CD.HQ_AREA_ID\n AND SVL.CATEGORY_ID = CD.CATEGORY_ID\n AND SVL.STATE_CD = CD.CUST_STATE\n
WHERE CD.LINE_OF_BIZ = 'CLOTH'\n
AND CD.HQ_AREA_ID is NOT NULL\n
AND CD.SOURCE_ID is NOT NULL\n
AND CD.CATEGORY_ID is NOT NULL\n
AND CD.CUST_STATE is NOT NULL)\n
update report_fct rpt\n
set service_level_id = P.service_level_id\n
from P\n
where rpt.case_detail_id = P.case_detail_id;"}
CREATE TABLE report_fct
...
..
case_detail_id bigint NOT NULL,
...
CREATE INDEX report_fct _ix1
ON report_fct USING btree
(case_detail_id)
TABLESPACE pg_default;
CREATE INDEX report_fct _ix2
ON report_fct USING btree
(insert_dt)
TABLESPACE pg_default;
One doubt I have is whether statistics can be skewed on this table which is resulting in degradation.
relname inserts updates deletes live_tuples dead_tupes last autovacuum last autoanalyze
report_fct 262746347 5387849450 0 2473523 3573914 5/19/20 3:38 5/19/20 1:13
EXPLAIN:
"Update on report_fct rpt (cost=24847.47..27881.35 rows=415 width=3772)"
" CTE p"
" -> Unique (cost=24844.02..24847.05 rows=405 width=16)"
" -> Sort (cost=24844.02..24845.03 rows=405 width=16)"
" Sort Key: cd.case_detail_id, svl.service_level_id"
" -> Nested Loop Left Join (cost=0.41..24826.48 rows=405 width=16)"
" -> Seq Scan on report_fct cd (cost=0.00..21915.21 rows=405 width=44)"
" Filter: ((hq_area_id IS NOT NULL) AND (source_id IS NOT NULL) AND (category_id IS NOT NULL) AND (cust_state IS NOT NULL) AND ((line_of_biz)::text = 'CLOTH'::text))"
" -> Index Scan using service_level_unq on service_level svl (cost=0.41..7.18 rows=1 width=45)"
" Index Cond: ((area_id = cd.hq_area_id) AND ((order_type_cd)::text = (cd.order_type_cd)::text) AND (source_id = cd.source_id) AND (state_cd = (cd.cust_state)::bpchar) AND (category_id = cd.category_id))"
" -> Nested Loop (cost=0.41..3034.30 rows=415 width=3772)"
" -> CTE Scan on p (cost=0.00..8.10 rows=405 width=56)"
" -> Index Scan using report_fct_ix1 on report_fct rpt (cost=0.41..7.46 rows=1 width=3724)"
" Index Cond: (case_detail_id = p.case_detail_id)"