So... I just came up to a post of a guy saying that each necklace level was giving his essences ~2% of increased power (either damage, shields, stats, healing...). So I decided to confirm it, and indeed, leveling up from 85 to 86 increased the essences' power:
https://ibb.co/album/mUoN3v
I tried to search if this was a bug or if anyone came up with this but I didn't find anything. Is this intended? Or is this a bug?