I'm running 15.04. Since latest updates few days ago of ubuntu base and kernel, I have incurred in the following issue, which only happens occasionally at some point (and to resolve it I have to restart):
When clicking on a icon in the unity launcher sidebar, the app won't open (some will 'flash' the glass background for a while, the cursor will show the 'loading' spinner while hovering unity sidebar, but no matter what, the apps won't start
When clicking/opening the dash and launching an app from the keyboard, the behaviour is the same, app won't start, if I move the mouse over the unity sidebar, spinning loader cursor appears for a while, no app open
In programs already opened, if I click on one link that is supposed to open a new tab in the browser (for example from Thunderbird message to Chrome), this won't work anymore, I need to copy and paste it
Existing programs will continue to work, unless I close them, after that the only way to restart is to restart the whole machine, until the problem happens again
Shortcuts to open programs (e.g. terminal) won't work (with some exception, e.g. nautilus).
I've seen sometimes the problem disappearing even without restart, after a while. But have no idea what triggers this. I can't open the task manager so I don't know what's running and if my terminal is closed I can't do much.
Tried reinstalling unity or compiz as already suggested but nothing changed. The system is stable, all the rest seems to be working fine.