if this isn’t a bug, it’s a massive oversight and needs to be addressed. I am almost at renown 12 with Loamm Niffen and I see that at renown 12 the Barter vendor, Ponzo, stops accepting Barter Bricks for the mount and the pet and instead only accepts Barter Boulders. you can buy the boulders for 3 bricks however the price for the pet and mount have not been cut properly.
currently costs 85 bricks for the pet and 170 for the mount. given that it’s a 3-1 ratio for bricks to boulders, the pet and mount should cost closer to 30 and 60 than their current prices of 40 and 85.