Ok, so when you have 20-30k shields, it is taken into account. But, your p4 is most likely the least stacked out of all of them in terms of defense/resistance. Let's say Naruto does 40k damage to your p4. The mystery description says deals 80% splash damage to units 1 grid away from the unit hit. 80% of 40k damage is 32k, meaning, your p4 will suffer 40k damage, and the remaining units will suffer 32k, sufficient to wipe your shields. It is not a bug. Splash damage is intended to work this way. My advice to you, next time, if you have Sage of Six Paths Naruto, aim for the opponents Ninja Dog Shiba or p3/p4.

Ok buddy, you did the math wrong. You know that the damage affects the shields first before hp. That's why it's called shield. Like Tyler said, the damage it does to shields doesn't show up on screen. If your p1 has 30k shield, and 61k hp which is 91k health, the 32k splash damage from Naruto removes shields first, leaving you with 59k hp. It's not a bug.

Ok, so maybe you didn't understand. I just used 40k damage and 32k splash damage as an example, because 80% of 40k is 32k, enough to wipe your shield. You say that your p1 takes full damage, so maybe that guy aimed at your p4, and got a critical. If your p1 didn't die, then he prolly did 70k damage. If your p1 did die, then he did above 75k damage.

6p doesn't need buff, he's already too op. If you have Y+1 power of six path passive, 15% ninjutsu everytime someone uses mystery. You can just add him with GNW Madara, Hashirama First Hokage, etc.