Describe the bug
Waited for ~1 hour, DR volume does not continue to restore after node reboot.

To Reproduce
Steps to reproduce the behavior:

1. Create a pod with Longhorn volume.
2. Write data to the volume and get the md5sum.
3. Create the 1st backup for the volume.
4. Create a DR volume from the backup.
5. Wait for the DR volume starting the initial restore. Then power off/reboot the DR volume attached node immediately.
6. Wait for the DR volume detached then reattached.
7. Wait for the DR volume restore complete after the reattachment.

Expected behavior
Should continue and complete restore after node reboot.

Log
longhorn-support-bundle_08642975-c7de-4048-975a-f900fdaecce8_2021-08-24T05-32-00Z.zip

Environment:

• Longhorn version: master
• Installation method (e.g. Rancher Catalog App/Helm/Kubectl): kubectl
• Kubernetes distro (e.g. RKE/K3s/EKS/OpenShift) and version: k3s
  • Number of management node in the cluster:
  • Number of worker node in the cluster:
• Node config
  • OS type and version: SLES15SP3
  • CPU per node: 4
  • Memory per node: 8
  • Disk type(e.g. SSD/NVMe): SSD
  • Network bandwidth between the nodes:
• Underlying Infrastructure (e.g. on AWS/GCE, EKS/GKE, VMWare/KVM, Baremetal): AWS
• Number of Longhorn volumes in the cluster: 2

Additional context
Add any other context about the problem here.