Part of Brinewater Grotto is used for the quest Scoundrel's Folly (TG04). The bandits are tied to the enable parent for TG04 and don't respawn. The bandit dog, however, does respawn due to a previous fix I would have to assume that it, like the bandits, was never intended to respawn in this particular location.
Maybe the issue can be addressed by linking the dog to the enable marker: pTG04BrinewaterBanditEnabler. This is how the bandits are handled.