Lost everything below Y level 1 in Caves Experimental

Didn't realize this until today since the overland chunks were also overwritten and there's snow everywhere, but everything below Y level 1 has despawned. Not a rendering issue as I was able to toss objects into the void. Previously I had dug down to Y level -25 and had been exploring a cave system. This world was generated in version 1.17.30 I believe.