I just noticed this: A Shaman has access to spells up to level 9 (pg. 256-257 of the Arcanis 5e Campaign Setting rule book). However, according to their slot level table (pg. 150 of the Arcanis 5e Campaign Setting rule book), the highest spell slot they ever get is 5th (class lv 9th-20th). Is this an error or do I have a hardcover book & PDF that got errata'd later on?

If it's not an error, how does a Shaman then learn any spells lv 6 or greater that is not granted via the class feature: Patron's Gift?

It's not an error. The shaman spell list for levels 6-9 is just the list of spells that can be granted by Patron's Gift.

(I'm nobody official, but I was tripped up on the same limitation. A shaman can't 'learn' a spell of higher level then their spell slots, per "Spells Known of 1st Level and Higher" on page 151. The Patron's Gift spells aren't learned. They're just granted as abilities to be used 1/day.)

It's all good. I keep forgetting that Shamans are Druids under Warlock 'guise hehe