Comment 4 for bug 1507558

Another recent patch that got us here is: https://review.openstack.org/#/c/215136/65/neutron/db/l3_dvr_db.py but it probably is not the culprit because it merely hides RouterNotFound exception, replacing it with silent debug log. There is a race condition mentioned in the comment, but it refers to a bug that corresponds to the patch intent, and does not give clue which race we experience.

Overall, it seems weird that we get RouterNotFound from the db.