I was testing the first 1.18 snapshot and I was curious to see if the Savanna plateau looks changed. I executed /locatebiome minecraft:savanna_plateau, but the game didn't find the biome in a reasonable range. So I tested with the Shattered savanna plateau, but I got the same message. I tried 10k blocks further in x and 11k blocks further in z. The game didn't find the biome. I repeated this 3-4 times, but every time I received the same message. Maybe it was this work, so I created another world, but both biomes were still missing from the generation.

I found this ticket, but I'm not sure it's the same bug.