Not entirely random, from what I've noticed.
I just beat Albus. At the first try I was like, "This dude is fucking OP!" But then I was like, "It's-a me, Mario!" and dropped his ass so hard. I thought the wind glyph was great on him at first, but then I used Vol Umbra and dude dropped like a rock, barely ever hitting me. Took me a few tries cuz I was always just dicking around, but I figured out his pattern after the 2nd attempt. Only times he gave me issues were when I did something stupid like stand try to kick straight down... and he'd kick straight back up.

Anyway, back on chests. Treasure chests. The higher the stage, the better the chest drops. In the first mountains, I'd get Iron Ores. In the second mountains, I'd get Silver Ores. In the mansion I'd get Gold Ores. Cashmere Thread was easy enough (Formors), but I wasn't finding any in chests until the mansions.
I also noticed there seems to be a super chest typically in the same places. I don't know if it's a random flag or if it just picks one chest on the map and randomizes it. But just keep going in and out of the stage and you should eventually get a super chest, which has a better drop.
But I'm finding a lot of my drops more easily from enemies lately, so...
Lemme think, boss I hated...... I hated Goliath. But then I equipped Ignis and um... the ice one... and just spammed the crap out of them and he fell pretty fast. But the bastard killed me so many times before that. I hated the crab, but it wasn't cuz the crab was hard, I just kept missing the platforms. Rusalka took me a while to figure out that I was supposed to stand UNDER the rocks. Gravedorcus pissed me off at first, but then I figured out to just stand on one of the ledges he makes until he tries to come at me from behind, then pummel his ass. ... Problem was I kept forgetting to get out of the way of his tail when I did that and there were so many sprites on the screen that I couldn't see me taking massive damage because i was standing right on top of him.
And yes, I beat Albus before finding all the villagers. >_> Fuckin' kidding me.... (got them now, btw. was missing the mom)