While playing in Quest Mode, my current random scenario had the "Goblin traited cards get a +1d4" modifier in effect. At one point I encounter a Goblin in the Warrens location. The game triggers the forementioned modifier rolling a 2, making the required Combat Challenge value 11. The very next instant the Warren's effect triggers which is if a monster is encountered, add a random new monster ontop of another location. Once that effect resolved on the Main Map, I'm whisked back to my current encounter in the Warrens but the Goblin's +2 bonus was lost and I was just shown the Goblin's normal 9 Challenge Value.

I had something similar happen to me yesterday, but I wasn't really paying much attention to what was going on so I didn't submit a problem I only had half the details for. Will have to check that out again today and see if I can reproduce your issue or any other strange behavior.

I would think the key elements are changing screens after some stock value is modified via a triggered wildcard (assuming that goblin modifier is a wildcard effect).