In one of our projects PHPStorm ran a while on 100% CPU, an investigation showed, that the process “checking for available composer updates” ran and used all the resources. Most likely it got stuck somewhere.
To get rid of the problem, one can turn off this feature. In IDEA Ultimate here:
[Settings] -> Languages & Frameworks -> PHP -> Composer -> “Check for available package updates”
And in PHPStorm here:
PHP -> Composer -> “Check for available package updates”