Try zmaul, nihilus, zylo, zavage, (any sith for last spot. I use zidious). Try to bait out enemy cleanse with basic attack debuffs before using AOE debuffs. Use annihilate on special enemies.
Try nightsisters. I use double zeta asajj ventress, NS acolyte, Old Daka, Talia, NS zombie. My NS zombie is g8 4 star. Try to get resets off asajj AOE when possible. Spread stuns out as much as possible+ tenacity down from zombie basic. Don’t ever use NS zombie special. and try to allow as many enemy taunts up before using asajj dispel. There is a little RNG hoping they don’t focus fire Daka but it’s a relatively safe strategy.
I’ve also had some success with cluster teams zeta Boba Fett lead with NS initiate (for crit up). Palpatine, tarkin, stormtrooper was one I can think of with them. Phasma works well too. TFP is decent too if you bring a taunt.
Conclusion. As others have said, it might be a mod problem. Or maybe you are trying to force certain squad combinations in that just aren’t working. Try mixing stuff up. Maybe try some squads I mentioned. I have finished all 4 waves consistently with those squads.