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.
[media]
MC-148148
Random chunks get regenerated
Resolved
Duplicate
0
João de Camões
(Unassigned)
Unconfirmed
Minecraft 1.14 Pre-Release 2
Retrieved
This was an issue in 1.14-pre1.