I play a bit in my world and suddenly there are chunks that are suddenly transformed and replaced like the ones illustrated in the pictures... The ones are on a fresh new seed of the same map while the holes are on the survival world I am playing in... Usually, some parts are changed into ocean biome chunks... hence the holes...
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Thank you for your report!
We're actually already tracking this issue in MC-150202, so I resolved and linked this ticket as a duplicate.
However, that ticket has already been resolved. Depending on the resolution, that can mean that it either will be fixed in the next version, or that it is not considered a bug and won't be fixed.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
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Thanks... I did indeed searched for it but none seemed to be immediately similar to what I've been experiencing... My bad that I didn't search thoroughly enough... Thanks for the swift reply...