In the second half of the series, they introduce the concept that Earth's atmosphere is poisonous to people from Crisis, killing them instantly if they don't go through a special treatment and they need a special atmosphere to survive, one that would kill humans. That directly clashes with many early episodes which show people randomly going from Earth to Crisis all the time.
They try to excuse that by briefly mentioning a treatment that the empire members go through before going to Earth, but, in earlier episodes, we also got many resistance members and random people from Crisis appearing on Earth - of course, in order to avoid people questioning that, the second half of the series never mentions the resistance members and Crisis civilians who escaped to Earth again, hoping people would just accept the different atmospheres explanation that they pulled out of nowhere.
And then there's the revelation in the final episode that Crisis was in a parallel universe and was identical to Earth and Earth could become a new Crisis in the future...and its atmosphere had been destroyed by pollution, which is presumably why they wanted Earth (all elements hinted at in the first few episodes, like when they mention that Crisis is distant from Earth, but at the same time not, and also talk about the emperor destroying Crisis' environment but ignored midway through for the whole "incompatible atmosphere" non sense).
