Where there any system updates? Windows security updates? AV updates? local firewall/IDS/IPS updates? IE or firefox updates?
What was your upgrade path? v10.5.1 directly to v11.x? What deployment software was used to update the DLP agents?
Sorry for all the questions. I am insterested as we are also on 10.5.1 will be updating to 10.5.3 in the next few weeks. and will be upgrading to v11 some time this year.