So, I was exploring the nether, looking for a fortress when I found these three. In case the screenshots are unclear, these striders are some 50 blocks above the lava lake they most likely spawned in. I don't actually know how these guys got up there, as I just found found them while climbing in a crimson biome and switched to spectator so I could get a closer look. Oddly enough, these striders are not only floating high above their lake, they're also in a stack of three, which I had thought was patched out in 20w18a.