Our team is working on a fix

Setting the API to Metal should fix it.
We don't support Mac standalone, so the setting shouldn't matter

Vuforia employee here - I'm seeing this same error with the same setup (Mojave, Unity 2018.14.1f1, Vuforia 8.1.1) - I've raised the issue with our engineering team and will get back to you when i get an answer

I also have the same problem and found a temporary solution by adding the below line in the Awake() function 

VuforiaRenderer.Instance.SetLegacyRenderingEnabledCondition(() => true);

from this link https://developer.vuforia.com/forum/unity/setlegacyrenderingenabledcondition

But I think this is a temporary solution and the Vuforia team should come up with a permanent solution for this problem.

Any luck vrjoy? i've got the same issue and spent two days trying to find a solution but nothing seems to be working :/