I am not quite sure why this is happening, but every now and again my application throws the following exception: https://github.com/symfony/symfony/blob/master/src/Symfony/Component/HttpFoundation/Session/Storage/NativeSessionStorage.php#L134

I can't work out why this would be happening. It happens about 10 times a day to a site which has quite a bit of traffic at the moment.

Any ideas?