The XP gained for completing part 10 (the ‘dungeon’ fight) of a chapter gives you significantly less XP than that of the other parts (eg: a skirmish fight).
Here is a screen shot of my part 10 fight at the end of chapter 3 hard mode:
for reference, I noted the xp for the fights running up to this one:
fight 1 of part 8 of chapter 3 hard mode, 206
fight 2 of part 8 of chapter 3 hard mode, 206
fight 2 of part 9 of chapter 3 hard mode, 208
considering it is a longer fight and with more enemies at a higher level, I would have expected more xp in return.