The world was fine in 19w14b (and posibly 1.14 Pre-Release 1 but not sure about that), but in Pre-Release 2, random chunks have been regenerated (completely replaced with new terrain). screenshot is attached.
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Environment
Minecraft Server, OpenJDK 1.8, MineOS (Based on Debian Linux), Intel Core i7 3770k
This was an issue in 1.14-pre1.