Just got a notification from Anna, there are some updates in the Wireless menu under the Bonus Box. We get more Bonus Teams under Fire Emblem (I've got 10 in total now) and a new section for Sacred Stones that only has a Seth team to challenge and we get a new item called Tyrfing; an A class sword that gives you +5 Resistance.
We've also got two more DLC quests in the Outrealm Gate.
That's probably the reason. I found the early chapters to be much more difficult than the others so far.
Earlier on in the game I used to 'huddle' my characters a lot more, pairing up also works as it allows weaker units to get in on some hits, earn some exp and build up your relationships faster which in turn will help you stay alive longer when it comes to teaming up against the enemy.
You should also try placing weaker units on forts, mountain peaks and the woods or anywhere else with a territorial advantage.