Redesigned the implementation of this bugfix to avoid unintended interactions and to ensure it works with all appropriate items even in Honour Mode. Thanks to Celes for the help.
Version 1.3
Fixed Necklace of Elemental Augmentation incorrectly augmenting the physical damage originating from weapon, instead of only the elemental damage originating from Booming Blade.
Version 1.2
Reverted previous update's fix attempt as it caused more bugs. I'll leave this fix as is until I figure this one out.
Version 1.1
Attempt to fix for this bugfix not always applying to Honour Mode difficulty. Let me know if you still see it doesn't work in Honour Mode.