If you have the Istio on GKE add-on enabled on a cluster, there is a known issue with the upgrade from GKE 1.16 to 1.17. Any custom resources you created in the istio-system namespace are deleted during an upgrade to 1.17 (R30 or earlier). These resources must be manually recreated. We recommend that Istio on GKE users do not upgrade to GKE 1.17 until a patch release fixes the issue. The fix will be rolled out in GKE release R31.