I was testing ways to make evokers stronger by giving them armor, when I noticed that the vex I didn't kill were not taking any damage after 2 minutes, I then did research about how long a vex can live without taking damage from non-entity sources (natural death) I saw that the max time a vex can live is 2 minutes, so I decided to report this bug. Please note that all these vex were summoned by an evoker as they only die naturally in that certain case.