I'm getting the following crash with Block Breakers:
https://pastebin.com/JTbGgUar

Minecraft 1.12.2
Version: ActuallyAdditions-1.12.1-r120.jar
Forge: 14.23.0.2493

Steps to Duplicate:
I was able to duplicate this with just Forge and ActuallyAdditions. No other mods.

1. Place Block-Placer
2. Place Block-Breaker facing the Placer, with 1 block gap between.
3. Place a couple stacks of Dirt in the Placer.

For me, it crashed right away in single player with the above crashlog.

I first noticed this with a modpack that recently upgraded to the above version of ActuallyAdditions. I have a setup that took coarse dirt, hoed it to create farmland, then used a block-breaker to pick up the farmland and get normal dirt. I had a similar setup with Bog Earth from Forestry that also crashed with block breakers.