It seems that there is something wrong with your iscsiadm configuration on the host nodes. Then the Longhorn engine cannot be launched.
The log of instance-manager-e-267e7e8b:
2019-12-13T10:18:44.421776548Z [pvc-1207e229-7320-4363-9bbd-a77fa03b568a-e-d7aef2b8-8e0c9333] time="2019-12-13T10:18:44Z" level=info msg="New data socket connnection established"
2019-12-13T10:18:45.47934259Z [longhorn-instance-manager] time="2019-12-13T10:18:45Z" level=info msg="wait for gRPC service of process pvc-1207e229-7320-4363-9bbd-a77fa03b568a-e-d7aef2b8-8e0c9333 to start"
2019-12-13T10:18:45.616282235Z [longhorn-instance-manager] time="2019-12-13T10:18:45Z" level=warning msg="FAIL to discover due to Failed to execute: nsenter [--mount=/host/proc/1535/ns/mnt --net=/host/proc/1535/ns/net iscsiadm -m discovery -t sendtargets -p 10.42.3.77], output iscsiadm: Cannot perform discovery. Invalid Initiatorname.\niscsiadm: Could not perform SendTargets discovery: invalid parameter\n, error exit status 7"
You can refer to this post to solve this issue. If it doesn’t work, feel free to ask for help.