So it produces paths like C:/work/mage2.pro/store/app/code//Magento/Backend/view/adminhtml/templates/menu.phtml
See on redundant (repeated) slash after app/code
.
The probjem method is \Magento\Framework\View\Design\Fallback\RulePool::createTemplateFileRule
How to fix it
See the code:
Remove the slashes after $themesDir
and $modulesDir
variables (at 4 places).