(sigh)

I'm relaying this on behalf of a user who I had to do a provide a SDK patch for.

For the Avatars SDK 3.6.1, in VRCSdkControlPanelAvatarBuilderV3.cs, Line 1993 contains the check for if the user is allowed to publish Avatars:

if (!APIUser.CurrentUser.canPublishAvatars)

This doesn't check if this is a test build, where rank doesn't matter, so the fix is:

if (!APIUser.CurrentUser.canPublishAvatars && !testAvatar)

Preventing untrusted users from building, especially locally where nobody is disrupted from it, discourages them from trying out VRChat Avatar creation. This is a very easy but helpful fix.