I recently removed a Maven module from my Intellij project. Shortly after, I tried to reimport the same module again, but somehow Intellij stubbornly refuse to show it in the Project panel. Eventually I looked into the MyProject.ipr file and found the module’s pom.xml file appeared in the ignoreFiles list.
[sourcecode]
<option name="ignoredFiles">
<set>
<option value="/path/to/my/module/pom.xml" />
</set>
</option>
[/sourcecode]
After I deleted the specific line with the pom.xml, I was able to reimport the module successfully again.