Do nodes become NotReady during a minor upgrade in OpenShift 4?

Issue

• During an upgrade, SDN pods restart, web console becomes unavailable, and nodes become NotReady for a brief time:

NAME                          STATUS     ROLES           AGE     VERSION
master-0.server.example.com   Ready      master,worker   4h25m   v1.14.6+9fb2d5cf9
worker-0.server.example.com   Ready      worker          4h25m   v1.14.6+9fb2d5cf9
worker-1.server.example.com   NotReady   worker          4h25m   v1.14.6+9fb2d5cf9

• This causes an outage, documented in the journal as NotReady message:

Sep 21 03:00:28 ip-10-0-140-173 hyperkube[1346]: I0921 03:00:28.784508    1346 setters.go:521] Node became not ready: {Type:Ready Status:False LastHeartbeatTime:2019-09-21 03:00:28.784452389 +0000 UTC m=+71.300956518 LastTransitionTime:2019-09-21 03:00:28.784452389 +0000 UTC m=+71.300956518 Reason:KubeletNotReady Message:runtime network not ready: NetworkReady=false reason:NetworkPluginNotReady message:Network plugin returns error: Missing CNI default network}
Sep 21 03:00:28 ip-10-0-140-173 hyperkube[1346]: I0921 03:00:28.785392    1346 event.go:209] Event(v1.ObjectReference{Kind:"Node", Namespace:"", Name:"ip-10-0-140-173.ec2.internal", UID:"ip-10-0-140-173.ec2.internal", APIVersion:"", ResourceVersion:"", FieldPath:""}): type: 'Normal' reason: 'NodeNotReady' Node ip-10-0-140-173.ec2.internal status is now: NodeNotReady
....
Sep 21 03:00:58 ip-10-0-140-173 hyperkube[1346]: I0921 03:00:58.812503    1346 setters.go:521] Node became not ready: {Type:Ready Status:False LastHeartbeatTime:2019-09-21 03:00:58.812452071 +0000 UTC m=+101.328956195 LastTransitionTime:2019-09-21 03:00:58.812452071 +0000 UTC m=+101.328956195 Reason:KubeletNotReady Message:runtime network not ready: NetworkReady=false reason:NetworkPluginNotReady message:Network plugin returns error: Missing CNI default network}