Sometime after I clear the dev cache with

php app/console cache:clear --env=dev

and then try to run some other command, like assets:install, I get an error like

  Notice: unserialize(): Error at offset [97 of 99 bytes in /var/www/html/vendor/symfony/symfony/src/Symfony/Component/Config/Resource/FileResource.php line 78

Although I have xdebug installed and enabled, it doesn't generate any backtrace.