Toxic Everywhere - annoying
Certain open world champions can be “infected” and receive the toxic buff. It’s pretty stupid imo.
Check for the little white-leaf-in-purple-box icon on certain Vets and Champs. If it’s active, you will find Hallucinations, etc.
Killing them was/is part of that patch’s Meta Achievement.
It is annoying but possibly in a good way. A lot of players get some enjoyment from beating challenging enemies. The toxic buff can increase the challenge and add interest to some of the more predictable fights.