Mana rifts - Hidden Archipelago

I feel like I am going insane. I'm trying to 100% the Underworld DLC, and all that's left are 5x mana rifts (and one resultant dig spot). 4x of them are on a cliff, assuredly to be accessed by the 5th one, at the plant lab. But the plant lab one just... isn't there? It appears to be at the fabricator for the plants elixirs, what has to be done to trigger it? I haven't seen any quests or lore notes indicating that I have to make certain recipes etc, and I have created all 3 of the base level plant extracts, as well as completing ever quest on the map for the DLC. Cannot find any info online :( does anyone have any idea how to trigger the rift appearing in the bio lab???