Owing showing zero balances, and cannot process payment

After upgrading an old SI installation to master_2019, I am having almost the same problem as in the locked “Owing calculation showing zero balances in error” thread. In my case, I am using preference_id 2 (no payment details invoice), and I attempted to apply the same fix, but owing is still zero for all invoices.

Additionally, I cannot process a payment – the dropdown for invoice ID is empty (no entries) and it’s a required input to the form.