I see you do have a compat hack already which tells RSO to ignore Cerys overall:
if mods["rso-mod"] then
data = data or {}
data.rso_ignore_planets = data.rso_ignore_planets or {}
data.rso_ignore_planets["cerys"] = true
end

Can you please remove marking RSO as incompatible?

Cerys generation has been reported as broken with RSO despite this compat, which at the time was the one recommended on the RSO mod page itself.

I’m happy for someone to submit a pull request fixing the compatibility.

Well, I'll be able to tell when I'll get to Cerys in my pt. But also judging by the fresh code I see in RSO that might be another thing needs fixing:
data.rso_ignore_resource_entities = data.rso_ignore_resource_entities or {}

maybe you'd need to specify ignore_resource_entities on top of ignore_planets and specify specific entity used on Cerys. I'll update when I'll get to it but idk when I'll be able to. I can confirm I did remove 'incompatible' from info.json and everything worked so far but I can't yet confirm Cerys correctly generated. Any easy way to test? Maybe with cheats console so I can go and test