Query much slower after upgrade to 9.6.1

Hello all, I have a query that was running quickly enough on 9.5.5 and has
slowed to a halt after upgrading to 9.6.1.

The server hardware is the same, 2 core, 4GB ram DigitalOcean virtual
server, running Debian 8.6.

The query is a pretty heavy reporting query to aggregate the dollar value
of "claims" against a specific "contract".

The query is below for reference.

Query plan on 9.6.1: https://explain.depesz.com/s/NwmH
Query plan on 9.5.5: https://explain.depesz.com/s/ioI4

We just migrated over the weekend, and this issue was brought to my
attention today.

SELECT
> con.client_id
> , 'product'::text AS type
> , p.product_number AS identifier
> , p.product_name AS description
> , civ.rebate_direct_decimal_model
> , civ.rebate_deviated_decimal_model
> , civ.rebate_direct_value
> , civ.rebate_direct_type
> , civ.rebate_deviated_value
> , civ.rebate_deviated_type
> , actuals.claimant
> , actuals.claimant_id
> , civ.estimated_quantity AS prob_exp_volume
> , COALESCE(actuals.rebate_allowed_quantity, 0) AS actual_volume
> , CASE WHEN r.rate IS NULL OR (r.rate < 0) THEN NULL ELSE (r.rate *
> civ.estimated_quantity) END AS prob_exp_dollars
> , COALESCE(actuals.rebate_allowed_dollars, 0) AS actual_dollars
> , COALESCE(actuals.transaction_date,null) AS transaction_date
> FROM contract con
> INNER JOIN contract_item_view civ
> ON con.contract_id = civ.contract_id
> INNER JOIN product p
> ON civ.product_id = p.product_id
> INNER JOIN product_uom_conversion civuomc
> ON civ.uom_type_id = civuomc.uom_type_id
> AND civ.product_id = civuomc.product_id
> LEFT JOIN LATERAL (
> SELECT
> claim_product.product_id
> , company.company_name AS claimant
> , company.company_id AS claimant_id
> , MAX(COALESCE(transaction.transaction_date,null)) AS transaction_date
> , SUM((civuomc.rate / cpuomc.rate) *
> claim_product.rebate_allowed_quantity) AS rebate_allowed_quantity
> , SUM(claim_product.rebate_allowed_quantity *
> claim_product.rebate_allowed_rate) AS rebate_allowed_dollars
> FROM contract
> INNER JOIN contract_claim_bridge
> USING (contract_id)
> INNER JOIN claim
> USING (claim_id)
> INNER JOIN claim_product
> USING (claim_id)
> INNER JOIN product_uom_conversion cpuomc
> ON claim_product.uom_type_id = cpuomc.uom_type_id
> AND claim_product.product_id = cpuomc.product_id
> INNER JOIN invoice
> USING (invoice_id)
> INNER JOIN company
> ON company.company_id = invoice.claimant_company_id
> LEFT JOIN LATERAL (
> SELECT MAX(transaction_date) AS transaction_date
> FROM claim_transaction
> WHERE TRUE
> AND claim_transaction.claim_id = claim.claim_id
> AND claim_transaction.transaction_type IN
> ('PAYMENT'::enum.transaction_type,'DEDUCTION'::enum.transaction_type)
> ORDER BY transaction_date DESC
> LIMIT 1
> ) transaction
> ON TRUE
> WHERE contract.contract_sequence = con.contract_sequence
> AND contract.contract_renew_version = con.contract_renew_version
> AND contract.client_id = con.client_id
> AND claim.claim_state = 'COMPLETE'
> GROUP BY claim_product.product_id, company.company_name, company.company_id
> ) actuals
> ON actuals.product_id = civ.product_id
> LEFT JOIN LATERAL gosimple.calculate_contract_item_probable_exposure_rate(
> (
> SELECT array_agg(row(x.contract_item_id, x.estimated_quantity,
> x.price)::gosimple.in_calculate_contract_item_probable_exposure_rate)
> FROM
> (
> SELECT
> civ2.contract_item_id
> , civ2.estimated_quantity AS estimated_quantity
> , AVG(pd2.price / puc2.rate) AS price
> FROM contract con2
> INNER JOIN contract_item_view civ2
> ON con2.contract_id = civ2.contract_id
> LEFT JOIN product_uom_conversion puc2
> ON puc2.product_id = civ2.product_id
> AND puc2.uom_type_id = civ2.uom_type_id
> LEFT JOIN price_default pd2
> ON civ2.product_id = pd2.product_id
> AND pd2.active_range @> now()
> WHERE TRUE
> AND con2.contract_id = con.contract_id
> GROUP BY civ2.contract_item_id, civ2.estimated_quantity
> ) AS x
> )) r
> ON civ.contract_item_id = r.contract_item_id
> WHERE TRUE
> AND con.contract_id = '54e28f3b-8f87-46fc-abf0-6fe86f528c0c'