It seems that Magnolia may ask to be restarted, when a module gets installed or updated. In such a case, the title on the installation screen changes to "restart required" and a message is generated asking for a restart. This message looks for a "restart icon", and since that does not exist, it fails with an error (see attachment).

I suggest we do the following:

• We show a warning icon also in case a module asks for a restart.
• For every module, which asks for a restart, we show an additional text in bold type shown on a separate line after the message and reading "Restart Magnolia to conclude the installation of this module."