Out of order chunk loading / corruption

(I'm putting in as much detail, hopefully it's helpful)

I have a singleplayer world, and when I loaded it up, for some reason all the chunks are glitched around (i.e. chunks from other biomes are present in my savanna area).  This has greatly affected my builds; half of my house is gone, my creeper farm is 80% gone, my villager "homes" are empty and partially cut off.  Certain areas are duplicated.  I have tried all the typical corruption fixes (pasting in new level files / session.lock files, looking for previous folder versions, etc).  I play with 1.15.2 Optifine.  I "mixed and matched" with creating new worlds and moving around level files.  I was able to get a world with the same seed and inventory and no chunk issues but no builds, and a world with builds, but broken by the chunk issues and no inventory.

I really love this world, and would hate to see the work go to waste.  

Thank you!