maybe a stupid question, but you installed the modules you trying to show correctly?
git clone MMM-blabla in the modules folder… and
after cloning most of the moduels need some dependencies
you need a npm install within the modules folder.
Just follow the readme instructions. Most of them are very cleraly described.
Maybe you should try to show the iframe module with a simple page like google.de?
Do you get errros that the mirror does not show anything at all, or just the new module is not shown?