Tried SLKR vs SLKR and both team members were impossible to beat forever. See the attached image. Note that the defending team had new DC level 15 for Night vision Rey. Other counters did not work ...
Ideas
This is a bug. I just mirrored with slkr and we went the full 5 min with all team members at 1%health (except the slkers due to ddamage immunity in ultimate allowing them to heal back up. Basically there is a bug that breaks this datacron in mirrors. You won’t be beating them with anything but SLKR or BANE for high end Kyber so if you lose with bane first then there is no counter left and you can stop playing. Between this and the Temple guard datacron bug I’m pretty frustrated with this particular gac fiasco.
Also, before saying this is working as intended is like defending the first time (only time) dodge datacrons were released where 100%+ dodge was possible (not the scoundrels). That was a fun gac and the content creators loved showing their teams missing unless they had an irresistible stun or unavoidable hit like SLKRs poke..
Bane didn't work for me - was not able to do the second turn and died. So this team is pretty invincible.