Confirmed as a bug:
However, the snapshot does not persist after getting hit within a GR and after 5s refresh from GW. The shielding value will revert to the appropriate level for the current gear worn in the GR after this type of refresh.
Therefore, the bug can only be abused in it’s current form at the beginning of a rift. After getting hit, the player would have to continue taking damage to maintain the higher snapshot shielding value.
Defensively, entering a high level GR on a push is one of the hardest times for a Wizard to survive.
While this could help a Vyr archon wizard start a GR much more smoothly, this does not help the wizard player long term in that same rift, as they would be taking considerably more damage, and it would eat through the shield stack, or reset, eventually.
Solo push is the mode of play most affected by this bug, due to partly affecting leaderboard rankings.
Group push could take advantage, however, it would be bothersome to reset every rift attempt while fishing (making your entire group wait).
Speeds, Nephalem rifting this wouldn’t be worth performing nor impact much.
So, while yes, it could affect LB rankings by some minor amount, it’s not critical. Perhaps medium to high priority fix.
As far as a fix is concerned: I would like to still have my Galvanizing ward shield stack ACTIVE at the beginning of a rift after a fix is in place. Entering a GR can be pretty dangerous on a lot of wizard builds.