P.S. Right after I clicked "Post", my thoughts went to "What about forage for the BG?"
If your pond was drained dry and all fish eliminated, then your panfish may not have much food available for them!
Did you add minnows ahead of time before your stocking, or just add some when you stocked your panfish and bass?
If you did the latter, then the panfish and the small bass might have cleaned out ALL of the minnows in just a few months. Very few people can afford to buy enough minnows to feed their fish for years on end.
The typical plan is to stock an empty pond with 10 pounds (or more) of fathead minnows per acre. (Depending on their size, that is 150-300 minnows per pound.) In a fertile, one-acre pond, those initial 2,000 minnows would turn into hundreds of thousands of minnows in a few months. Then the panfish and bass are introduced. By the time they have eaten up all of those minnows, the pond should have good reproducing populations of your panfish and bass.
It is much tougher to introduce minnows after the larger fish are already in the pond. They typically get eaten before they get to massively reproduce.
If you did NOT have a big minnow population before your initial stocking of other fish, then that alone is almost surely that cause of your disappointing results. Initially your BG only had some insect larva to eat. Now they get some fry from the bass, the RES, and the other BG, but that is not enough food supply.
