I created a Toad View and put it in a single-connection query builder and got over 12K records in my results when I selected Fetch ALL Rows. I took that same Toad View and put it into a cross-connection query builder (with no other changes). Again, I selected Fetch ALL Rows, only this time only 1,092 records returned. I found an old entry (e.g. 2014) in the Toad World forums where another user had this same issue. The resolution suggested for that user was to upgrade his Oracle Client Drivers to 11g/12c (he was using 9). That solution doesn't work for me since I am already using 12c.
BTW - I am currently using TDP ver 188.8.131.52 64-bit.