This bug is only partially fixed. Can still replicate loss of structure information every time.
Open existing 1.15.2 world, enter nether, use /locate fortress and the fortress which is < 100 blocks away is detected.
Open the same 1.15.2 world in 20w29a, enter nether, use /locate fortress and the fortress which is < 100 blocks away is not detected. The closest fortress found is in the nearest newly generated 1.16 chunks. The same issue can be repeated when opening the world in 20w27a for the first time when upgrading from 1.15.2.
This bug is only partially fixed. Can still replicate loss of structure information every time.
Open existing 1.15.2 world, enter nether, use /locate fortress and the fortress which is < 100 blocks away is detected.
Open the same 1.15.2 world in 20w29a, enter nether, use /locate fortress and the fortress which is < 100 blocks away is not detected. The closest fortress found is in the nearest newly generated 1.16 chunks. The same issue can be repeated when opening the world in 20w27a for the first time when upgrading from 1.15.2.