So I was going SLKR, Rey (DSV), Hux, Sith Trooper & KRU vs a replica team, w/ a couple of relic differences, and I ran into the issue of both sides being un-killable & both Reys not losing their untargetable throughout the battle.
Sounds similar to this old issue I found from November: https://forums.ea.com/idea/swgoh-bug-reports-en/first-order-invincible/12922985
I've attached a screen recording of the last 2min of gameplay. Hope it helps...