Server does not save any placed blocks and reverts them back after a while.

Hello! Ive been having an issue with a server I created. The world for the server was a modded world, but this server doesnt have any mods installed. So naturally all of the modded blocks were deleted. Id wanted to let the game remove them itself, as opposed to spending countless hours doing it myself, and was glad when the server loaded with all the blocks removed instead of having a missing item in their place. As I began to replace the blocks manually, I noticed that if I left that location for a long period of time and came back (effectively reloading the chunks) or if I restarted the server, that the blocks I had placed were being removed. Initially I believed that this might be because the game was trying to replace the empty space where the modded blocks used to be, but since those blocks werent in the server, it just reverted them to air. However, when I decided to make a new build, I found out, much to my dismay, that the server didnt save the blocks placed in that build either once I logged into the server a day later. This has essentially softlocked the game for me. Is there a way to use my current world on the server or would I have to make a new world? Thanks a lot for the help!