Invincible enemy not allowing me to complete the remnant

https://reddit.com/link/1tz2hfn/video/4sdqvypphs5h1/player

Pretty much as the title says, I've had this particular enemy (not the rare, the minion that spawns from it) be invincible/Untargettable every time it spawns, so I cannot kill the little minion to kill the rare and therefore cannot complete the encounter. This has already happened to many countless times. Any fixes?