Forge version:
14.23.5.2855

HAC Mod version:
1.12.2-3.6.8

HAC Lib version:
1.12.2-3.6.6

How to reproduce:
Simply put HAC Mod and Twilight Forest Mod together in a modpack,
then search Twilight Forest dimension for boss spawners.
You will find some spawners for Hydra and Alpha Yeti have become HAC ores.

If you need screenshots, I will provide it later, sorry for any inconvinience caused by me!
Thanks for your help in advance!

There is already a blacklist option for adding blocks that the player does not want to replace. Please use it.
("Blockgen Disable List" in worldgen.cfg)

Got it. Thanks for your explanation!

Special blocks, such as those with TileEntity or no drop items, are not replacement targets for ore generation. But otherwise, if the implementation is internally indistinguishable from a naturally generated normal block, HaC will not be able to identify it. They can be individually excluded by the player.

There is already a blacklist option for adding blocks that the player does not want to replace. Please use it.
("Blockgen Disable List" in worldgen.cfg)