My friend stopped hosting his Realm and gave me a backup of the world to self-host.
I've tried two different backups but the end result is that everything in the negative X direction is getting reset to what the seed was like at the start, and the positive X direction was left completely alone.
All I've really done is change the game mode and place the backup directly into the World folder, since that's all the content that existed from the backup.
Also, the same thing happens if I copy it to the single player world folder. I tried to Optimize that version in the Edit options, but all that did was change the Negative X direction to the New World seed.
Any suggestions here? Most of our stuff was sadly in that direction cause positive was coastline...
Well, I found a solution to the problem. Albeit not a perfect one.
I mapped out what regions were needed to keep the most amount of changes made to the server from a player perspective. After making a list of about 16 regions, I deleted ever other region file in the world folder. I also grabbed new, uncompressed versions of those files from the Realm and replaced them. This set everything except those regions back to stock, and let the server populate the most heavily used regions without an issue.