Oracle 12c - Opening cursor with remote tables over db link

We just upgraded from 11g SE to 12c SE. Please note, this process worked perfectly under 11g, and only started failing once under 12c. The procedure puts together a query, and then opens up a REF Cursor to return the data. The query has remote tables which are accessed via DB Link. If I take that query by itself, and paste it into SQL Plus, it works fine. But, if I run the procedure, and try to print the REF Cursor, it just hangs, forever. What changed between 11g & 12c to make this start failing?