I've noticed 2 issues with opponent AIs in my Normal difficulty Stellaris game so far:
- My neighbor (who I'm allied with) nearly starved himself to death. He was down to just 16 pop over 5 worlds. Once I started giving him 100 Food monthly, his population tripled within a decade.
- A civilization at the very edge of a spiral arm hasn't expanded to a 2nd system. At all. In over 100 years. And it's not because he was crowded out because the nearest civilization (me) was in another arm entirely.