The Woot mob grinder sometimes gets into a state where it continuously deletes blocks in a 3x3x3 volume centered on the structure starting at the bottom bedrock layer. It appears that it deletes any blocks (including bedrock) in that volume at spawn rate.

This issue was seen in FTB Beyond with ChickenChunks added. This happens whether the grinder spans chunks or is entirely within one chunk.

It is a workaround for a known issue and should only happen while a mob is being learned. I've bumped that to a skybox in the latest release to try and lessen the impact.

I encountered a similar issue with the latest FTB Beyond beta version: Everytime I destroy a block near the grinder, it gets sucked in and the grinder starts to spawn it besides the regular mob drops.

Don't think ftb beyond has moved to 1.10.2-1.3.1 yet, which is where the change was made.
I had made a huge mistake in one of the calculations that caused this.
Recommend that when they use 1.3.1 you run /Woot flush all
That will reset the loot tables that I have learnedSee #182