Two separated teams. Team 1 is battling minions on their starting tile, and team 2 explores into that tile for the first time. There is a special setup (minion placement) for that tile at game start (i.e. for team 1), but no special setup rule for when team 2 explores the tile.
When team 2 explores into the tile, does that trigger a new encounter? (I.e. encounter card is drawn and new minions are placed in addition to what's already there?)
The rules state that an encounter card is drawn when a "previously unexplored tile" is explored, but it is not clear whether a tile that has mice and minions can count as "previously unexplored" or not.
PS This is the situation in Chapter 5 of HoG, but other chapters may have similar situations.
I believe a "previously unexplored tile" is used to describe a tile where you haven't been before with any party. I don't have the Glorm storybook at hand, so I can't check your specific situation, but you probably don't need to have a new encounter there.