It was so weird when I was playing last night. Went through 3 battles with 0 drops and then like 7 or 8 dropped all at once on the next one. And hitting random barrels sometimes yielded 2 or 3.

I thought maybe doing an event might get more drops but no, not really. It just got me killed. :P I did better just roaming the countryside. By the end, I began wondering if the drop rate depended on the type of monster? I felt like I was doing better with spawning types like shamans and worse with ghosts? But who knows? I guess if it's a bug, it's all moot at this point.