Seems to be a general bug in professions. Even with 100% I occasionally get regular non-+1 results. I've had it happen with potions and refined materials. Happens with the gond hammer tool and with legendary tools.
More info, think I might have done this... With Mythic Gondhammer. Did some armor kits with that Tinkers supplement. Noticed it was producing kits not +1. Took Tinker supplement out, just assumed it was feature of supplements. But even with Tinker cleared from slot, now still producing not +1 kits.
Has this been fixed in the latest patch? I've been getting consistent +1s again since yesterday (did not apply to delivered products in the chest from before the patch but everything I crafted afterwards). Also, the buttons to instantly finish a product with morale work again more than once.
I haven't tested with a forgehammer but the delivery bug seems fixed as of yesterday. The +0 items bug actually stopped affecting 1 character a few weeks ago, but was still aftecting my main, with the forgehammer.
"We have always been at war with Dread Vault" ~ Little Brother
Answers
With Mythic Gondhammer. Did some armor kits with that Tinkers supplement. Noticed it was producing kits not +1. Took Tinker supplement out, just assumed it was feature of supplements. But even with Tinker cleared from slot, now still producing not +1 kits.
This is uber annoying.
professions with 100% chance for +1 results in 20-30% +0
1) it happens both with and withou forgehammer
2) supplement have no impact as well