Before the patch the super soldier only checked to see if the shield changed value to be at max capacity, whether that was recharging up to full capacity or moze loosing phalanx doctrine stacks while at full capacity meaning she would go from a higher max capacity to a lower one, and the shield on deactivated the effect when you would go below max capacity.
Moze could the stack the effects by loosing phalanx doctrine stacks while at max capacity so it would re-trigger the activation by the value changing to the new max but not trigger the deactivation because she was always at max capacity.
Fl4k and moze could also permanently keep the effect active by using an amp version to reduce the capacity while invincible and then fl4k could use fuzzy math to restore it and moze could use bloodletter and health regen to keep it up which then for both of them would continually bring the shield to max value and re-trigger the incinvibility but this wouldnt build up multiple stacks since the capacity would be decreasing. Personally I feel this is a fair use as its a specific build setup for it to work and its then rewarding you for keeping the shield filled
Gearbox managed to bust the shield by making it work similarly to the stop-gap where if the shield reaches max capacity triggering the effect while the effect is already active it then just deactivates for the time that it would normally be active for, 5 seconds I think, and cant be reactivated till the time is up, meaning you dont want to have the shield constantly drain and refill with an amp version as it’l break the effect and deactivate, and if you use Action Skill Start anointment on the shield you only want to trigger it once the effect is over.
They also nerfed the shield’s move speed, ammo regen and fire rate around when it was released due to moze’s unlimited stacking but havent reverted this change making it was less useful than it was before which sucks as there are ways to use it reasonably well, like a non amp version on fl4k with fuzzy math so that whenever the invincibility deactivates and the shield drops from max capacity fl4k can very quickly fill it back up to max starting the invincibility again and will then remain at max capacity while invincible since they cant be damaged