It is not possible to take enchantments off of modded items, such as those from RPG Series some modded items, while it takes off from others. In the case it doesn't work, both the item and the book can be placed inside a grindstone, and a possible output book with enchantments will be present, but it can not be taken out of the grindstone, instead infinitely going back to the output.

Seems that my game was bugged and it didn't properly show how much levels it requires to grind them off, showing much less than it should be. Closing this issue as it is completely invalid.