Certain seeds either excessively using 1 tree type or not giving trees at all.

So I was recording a video of 1.16 Release Candidate 1 for my YouTube channel (as I'm writing this I'm still recording but this is not on screen, yet) and the first time I create a hardcore world I spawn in a world consisting of mainly birch trees, I only found so much of oak and spruce (not much). It took a while for me to not see birch anymore and to get to normal land, and then I get killed by a spider. Whoopee. I make another hardcore world, then it's just island and 3 pigs. I roam around a bit and there's just... no trees. I do some swimming around in the water and then I find an ocean monument, BAM, impaled by a baby Drowned. The deaths aren't the bug though, it's the generation of the worlds, possibly. I make another world and it seems quite normal, but then when I dig straight down (which of course breaks the number 1 known rule) to find a cave, a Zombie decides to hop down in there with me for fun and I die. I was just about to get iron hardware. But anyway, back to the point. First world I got was 98% birch trees, next world was 100% land and water (and somewhat ice), next world was normal. What an experience. Not so much in a bad way but I think hardcore just got harder.