Damage reduction effects normally stack multiplicatively. For example, if I use Hardened Armor, which grants 35% damage reduction and my opponents gets deflected (60% damage reduction), the total damage dealt should be 0.65 * 0.4 = 22.75% (or 77.25% damage reduced).
In the case of Titan's Shroud, the damage reduction is 30%, so with a deflection, the damage dealt should be 0.7 * 0.4 = 28% (or 72% damage reduced). 28% is still a lot! If I did an attack that would have done 500 damage, I should still be able to hit for 140.
But that's not the case at all. No matter what I test, no matter how strong of an attack I use, getting a deflection on Titan's Shroud instantly reduces the damage to the minimum of 30. This can be very overpowered over the course of a long fight.
The most extreme scenario I tested in a challenge fight was with a 740-810 +88 (Deadly Aim) damage sidearm using Blood Bullet (+20% more damage) against 93-106 defense. The base damage for this attack is 994-1078, so the damage after defenses is 888-985 when no other effects are at play. A normal deflect did around 370 as expected. With Hardened Armor, deflections hit for about 240, also as expected. With Titan's Shroud, it hit for 30 every time. That is way off. There are even more extreme examples that I could test, but there's no need to go through the trouble when it's already clear something's not right.
In trying to figure out what the actual problem was, I initially thought that maybe the damage reduction was being applied additively here, i.e. 30% + 60% = 90% damage reduction. But that can't be the case because even 10% damage of 888-985 is nowhere near 30. Based on my data, it may as well be 100% damage reduction, and I don't know why.