Existing chunks are being replaced by new chunks

BUG REPORT: MY 6 YEAR LARGE CITY HAS BEEN DESTROED BY NEW TERRAIN DAWG !!! Me and 2 other lads spend nearly 8 years working on a huge city day and night, constantly sending the file back and forth to eachother, backing it up with all our might and making sure the files aren't corrupted.. No matter how much times we back up our files for the latest update, our world continues to load new chunks replacing our builds or removing them entirely. Sadly, this update screwed us over and we can't report it to MC feedback due to the new verification EU feature and our ID's don't work for some reason to verify that we are adults. I don't know what to do atp. Seems Hundreds of individuals been reporting this same problem aswell and I guess we aren't the only ones... Mojang better do something about this