Sorry I couldn't provide backtrace with debug symbols…
Regarding proposed packages:
To be sure, I went back to the old versions of packages unity, unity-services and libunity-core-6.0.9 (7.2.5+14.04.20150521.1-0ubuntu1), reboot, crashes are back.
Then I installed the proposed repository, updated the three packages to latest version: 7.2.5+14.04.20150603-0ubuntu1, reboot, no more crashes.
Sorry I couldn't provide backtrace with debug symbols…
Regarding proposed packages: 14.04.20150521. 1-0ubuntu1) , reboot, crashes are back.
To be sure, I went back to the old versions of packages unity, unity-services and libunity-core-6.0.9 (7.2.5+
Then I installed the proposed repository, updated the three packages to latest version: 7.2.5+14. 04.20150603- 0ubuntu1, reboot, no more crashes.