I don't really know what stats the enemies had before, but they were dealing way more damage than before. Comparing them to the stat points available to my characters they had around 6 points more (Garnet had no HP upgrades and ATK: 19 | Def: 11 at level 18). The bat stats would probably have been something around [ATK: 19 | Def: 11], however I could be wrong here. It just seemed like they were way stronger than before, seeing as my whole team (Garnet (18), Peridot (18), Jasper (18) and Stevonnie (19) ) was almost defeated by four bats at level 17.
Regarding the cleared areas: I played pretty much straightforward. I've completeley cleared the strawberry battlefield and the barn, including all treasures. Lapis says I have 2 more treasures remaining in the Kindergarten, so those didn't reset, it seems.
This is not the first time I've reloaded/loaded a save, but probably the first time where I had after manually putting stones in the door slots and having left them there.