Humans tend to try to find pattern in randomness, which is what you're trying to do. From a statistics point of view, it fits in the randomness. In case you're wondering, I run 20-1 a lot and I see all types of drops. One recent run, all I got was 1 Animaton. Just 1, and nothing else. There's about 120 enemies in 20-1, and each, on average, has a 6% chance to drop one item (approximately). So a normal run without treasure hunter, it's probably about 7.2 items (plus 0.8 for rare ores + moon tears), you're expected about 8 items. You're getting more than that, on average. Do a few more runs, and keep track of the results, and I'd like to know if you feel like you aren't getting drops. Good luck!