Minecraft wiki entry for Development_versions, associated text: Slightly changed datapack loading to prevent custom datapacks from crashing.
If datapack reload fails, changes are not applied and the game continues using the previous data.
Changes to datapack list are stored only after a successful reload.
If existing datapacks prevents the world from loading, the game offers the option to load the world in safe mode, which loads only the vanilla datapack.
Added --safeMode option for servers to load only the vanilla datapack.
Game now detects any critical datapack issues, such as required tags being missing, and prevent the world from being loaded.