The upgrade to 6.0.2 was doing the same thing, but
suddenly was visible by the update system.
Never figured out why, as it worked.
Anyway, yes, I was attempting to install from a sub directory in the TMP folder, as this is what I normally do, to keep things as clean as possible.
So I tried directly in the TMP folder (after opening), and that didn't help either. Still the warning stuff and error.
But, I tried to install Matukio a few minutes ago, on a clean test site (only template installed to the Joomla 3.5.1), and even there, Matukio will not install.
This is the Matukio once opened... shouldn't it have at least an XML file at this level?