I'm probably not the only one who has this theory/assumption but to me it's pretty heavy evident that Halpha is actually planet Naverius.
The biggest clue is the fact that Sylvants are native to Aelio. It could be possible that the Sylvants were an introduced organism to the planet at some point in ARKS thousand-year gap but given how ARKS treat sylvants in PSO2 I doubt they would go to the effort to preserve hostile species.
The second clue is that beyond North Aelio appears to be a polar region which doesn't make sense given the climate temperatures and weather of the rest of Aelio. In PSO2 it's been noticed the Tundra region on Naverius baffles most ARKS ops in comparison to the Forest region. The Alphana Wetlands have ruins that also bare resemblence to the sunken Ruins of Naverius which further makes me curious of Halpha's history.
Some would perhaps ask "If Halpha is actually Naverius, why can't I access the PSO2 areas?", well for all we know those areas could be on the other side of the planet and that they may have changed after a thousand years. In PSO2 we only explored small regions of the entire planet so they could be on the other side of the world. It's like how Earth is depicted in PSO2 with just parts of Tokyo and Las Vegas.
So all in all, my guess is somewhen during the thousand-year gap, ARKS decided to colonize Naverius and over the faded history the planet was renamed Halpha.