[Zelkyri]

The bosses give no verbal clue before using Banish. if you're close enough to cast Shield Breaker on them they're able to physically attack you since Shield Breaker has a very poor range. It's impossible to run out of the Banish's range if you're caught in it while casting Shield Breaker if you have no sprint.

Basically when you use Shield Breaker on
Neutral monsters : Damage still increases
Gun weak monsters : Damage will greatly increase
Gun resist monsters : Damage will increase
Gun damage absorbing monsters : Null the absorption and you'll be able to deal damage with the gun. Although the damage dealt isn't as high as compared to other monsters under the Shield Breaker debuff.