Maps Have Weird Blocks On Them

Hi there. I run a Minecraft SMP server and we just finished our second season. Normally at the end of the season, we like to release the world map to our viewers to play on. I was waiting for the full 1.16 release because I noticed a weird map glitch where it looks like a bunch of stone blocks and lava are covering any newly generated maps. This has technically been occurring since 1.16 pre-3. Please fix this issue.