The current definition is:

     * @ORM\Column(name="session_id", type="string", length=255)
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")

It doesn't make sense to put "AUTO" there as this column shouldn't be incremented. This definition can cause problems for example with running:

php bin/console doctrine:schema:update --force

as it would alter this column all the repeatedly.