Was bonemealing my flower forest biome to reveal the natural flower growth patterns and I came across this patch of grass that refused to grow anything.

Im refering to that continuous patch of grass blocks the screenshot is centered

Current actions/observations

Already researched the issue, results were mostly inconclusive
Only suggestion was a bug that didn't allow bonemealing of grass blocks under cave air
I suspected I might have patched a cave up under it but upon review the closest cave is over 40 blocks deep
This is a survival world with 700+ hours
This world was created pre-caves & cliffs
This chunk was generated when I initially created the world and is not on an update border
I used more than a stack of bonemeal on the blank area