Failed Nuclear Explosion created permanently loaded chunks

[SwiftSniffer]

Following the detonation of a Nuclear Bomb, and due to messing with its power setting and the fact that it loaded a huge amount of entities and what not (I'll skip the details), this caused the world to crash.

Upon reloading, the explosion did nothing (except a small tnt explosion), and ever since then, all chunks within the bomb radius are permanently loaded.

Removing chunks with the /forceload command did nothing, because apparently no chunks are permanently loaded. Removing the mod did nothing.

Is there a way to fix that? It hammers the performance of my world. And I can't just delete the world, nor can I do anything about the content of those loaded chunks.