Once you begin New Game Plus, you can unlock more than the original twelve total Implant Slots through more Core Levels (100 onward). The bug is the fact that these new slots don’t actually appear in the implant menu, even though they’re there. You can equip more than twelve implants and utilise these additional slots, but due to being unable to see them, you cannot unequip any implants you place in these slots.
Additionally, these can carry across different characters/saves. I equipped Pain Enhancer for one save data in the 13th Implant Slot of Loadout 1, and now Pain Enhancer is active on Loadout 1 of all my saves. I cannot fix this until these NG+ Implant Slots are made visible.
Thank-you for the post launch support so far, the game is amazing aside from a few issues!