1.14-pre2. World has been transferred from 1.13.2 and "optimize world" feature doesn't seem to help with this issue. After first attempt to transfer this world there's been dark chunks on the lake (fourth screenshot) but not after second transfer (third screenshot)
edit: during first transfer I tried to optimize world (with checked "erase cached data"), but not during second one
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Partly. World is playable in 18w30a but optimizing isn't working, it's just seems to stuck at random chunk everytime, at least for me. In 18w30b all is ok
Fixed in 18w30b
Only vanilla, yes. 1.12.2
edit: this world is playable prior to pre-7
Screenshot with F3 screen. Also, I cannot reproduce this bug while in singleplayer mode
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