I am having the same issue (on 1.16.1), and the world was first made around 1.14ish (although I can't be sure, but it was definitely made pre 1.16). I will make a video soon showing off the problem to as good of a detail as I can provide. Otherwise everything is practically the same as the original report.
Also some things to note about my case in particular which I feel like I should mention:
I had recently done a fresh install of Minecraft after a hard-drive wipe, and this world was plucked from my disk backup into my fresh install of Minecraft
I have Minecraft installed on a different drive than the AppData folder. All the usual files that would normally exist in AppData are still put there (in fact I'm not sure there's even a way to move them from that directory without maybe a symbolic link), but the install itself (maybe just the launcher? not sure) was put into a different drive.
I have no idea if any of the above is relevant, but I only started getting this issue after my fresh install of Minecraft, and the issue existed even on 1.15.2 (but only after the bulleted things above were done, before that everything worked fine), so I suspect there's something wonky with either pulling the world data from a different install of Minecraft, the backup I did of my drive somehow slightly corrupted my world, or having Minecraft installed in a different drive from AppData is causing something to go wrong.
Please let me know if any more information is needed.
Nicholas Kane
I am having the same issue (on 1.16.1), and the world was first made around 1.14ish (although I can't be sure, but it was definitely made pre 1.16). I will make a video soon showing off the problem to as good of a detail as I can provide. Otherwise everything is practically the same as the original report.
Also some things to note about my case in particular which I feel like I should mention:
I had recently done a fresh install of Minecraft after a hard-drive wipe, and this world was plucked from my disk backup into my fresh install of Minecraft
I have Minecraft installed on a different drive than the AppData folder. All the usual files that would normally exist in AppData are still put there (in fact I'm not sure there's even a way to move them from that directory without maybe a symbolic link), but the install itself (maybe just the launcher? not sure) was put into a different drive.
I have no idea if any of the above is relevant, but I only started getting this issue after my fresh install of Minecraft, and the issue existed even on 1.15.2 (but only after the bulleted things above were done, before that everything worked fine), so I suspect there's something wonky with either pulling the world data from a different install of Minecraft, the backup I did of my drive somehow slightly corrupted my world, or having Minecraft installed in a different drive from AppData is causing something to go wrong.
Please let me know if any more information is needed.