tpcds query78 alternately fails and works with incorrect results

#QUERY_78

with ws as

  (select d_year AS ws_sold_year, ws_item_sk,

    ws_bill_customer_sk ws_customer_sk,

    sum(ws_quantity) ws_qty,

    sum(ws_wholesale_cost) ws_wc,

    sum(ws_sales_price) ws_sp

   from web_sales

   left join web_returns on wr_order_number=ws_order_number and ws_item_sk=wr_item_sk

   join date_dim on ws_sold_date_sk = d_date_sk

   where wr_order_number is null

   group by d_year, ws_item_sk, ws_bill_customer_sk

   ),

cs as

  (select d_year AS cs_sold_year, cs_item_sk,

    cs_bill_customer_sk cs_customer_sk,

    sum(cs_quantity) cs_qty,

    sum(cs_wholesale_cost) cs_wc,

    sum(cs_sales_price) cs_sp

   from catalog_sales

   left join catalog_returns on cr_order_number=cs_order_number and cs_item_sk=cr_item_sk

   join date_dim on cs_sold_date_sk = d_date_sk

   where cr_order_number is null

   group by d_year, cs_item_sk, cs_bill_customer_sk

   ),

ss as

  (select d_year AS ss_sold_year, ss_item_sk,

    ss_customer_sk,

    sum(ss_quantity) ss_qty,

    sum(ss_wholesale_cost) ss_wc,

    sum(ss_sales_price) ss_sp

   from store_sales

   left join store_returns on sr_ticket_number=ss_ticket_number and ss_item_sk=sr_item_sk

   join date_dim on ss_sold_date_sk = d_date_sk

   where sr_ticket_number is null

   group by d_year, ss_item_sk, ss_customer_sk

   )

 select 

ss_sold_year, ss_item_sk, ss_customer_sk,

round(ss_qty/(coalesce(ws_qty,0)+coalesce(cs_qty,0)),2) ratio,

ss_qty store_qty, ss_wc store_wholesale_cost, ss_sp store_sales_price,

coalesce(ws_qty,0)+coalesce(cs_qty,0) other_chan_qty,

coalesce(ws_wc,0)+coalesce(cs_wc,0) other_chan_wholesale_cost,

coalesce(ws_sp,0)+coalesce(cs_sp,0) other_chan_sales_price

from ss

left join ws on (ws_sold_year=ss_sold_year and ws_item_sk=ss_item_sk and ws_customer_sk=ss_customer_sk)

left join cs on (cs_sold_year=ss_sold_year and cs_item_sk=ss_item_sk and cs_customer_sk=ss_customer_sk)

where (coalesce(ws_qty,0)>0 or coalesce(cs_qty, 0)>0) and ss_sold_year=2000

order by 

  ss_sold_year, ss_item_sk, ss_customer_sk,

  ss_qty desc, ss_wc desc, ss_sp desc,

  other_chan_qty,

  other_chan_wholesale_cost,

  other_chan_sales_price,

  round(ss_qty/(coalesce(ws_qty+cs_qty,1)),2)

limit 100;