Grand Garden seam is not natural area.

[Disorder]

Upon entering I've been getting message that area is unnatural. Bonuses classes like ranger / druid should get do not apply.

I am not certain about quest areas there, but main on certainly is not natural.

Can it be fixed?

[Arslefjun]

Grand Garden Seam.
Seam is key here.
That means you are in another plane outside of the natural world which in turn makes the area unnatural even if it is a "Garden".

[Disorder]

No shit? Then why moldmire seam and grand fissure are natural places?