With 2.4.1, after every battle the party order is offset such that the back moves to the front and everyone else moves back a space.
E.G. [4 3 2 1] => [3 2 1 4] or if you only have 3 in party [3 2 1] => [2 1 3]
Edit: This isn't perfectly consistent... I had the above case for three dungeons in a row, but this dungeon has been [4 3 2 1] => [4 2 3 1] after every battle.
The only difference might be class composition?
For the first three I had; [Mage Rogue Cleric Warrior] lineup
For the most recent one: [Ranger Mage Cleric Prisoner] lineup
Viewing post in Ero Dungeons [Old Version] comments
I had the impression that the post-battle party lineup is influenced by the characters and their classes and levels. At least it only changes once I level up or switch one of my characters and also returns to the previous lineup as soon as I switch back. Otherwise I can see little logic behind it. It doesn't depend on hp and durability, but it seems to prefer prisoner, cleric or rogue at the forefront