Pre Ready-For-Testing Checklist

Where is the reproduce steps/test steps documented?
The reproduce steps are at: [BUG] kubectl drain node is blocked by unexpected orphan engine processes #6552 (comment).
The test steps are at: fix: attempt to delete processes from instance-managers in unknown state longhorn-manager#3127 (comment).
Is there a workaround for the issue? If so, where is it documented?
The workaround is:
Verify that ONLY extra processes are running in the instance-manager, then directly delete its pod.
Does the PR include the explanation for the fix or the feature?
Have the backend code been merged (Manager, Engine, Instance Manager, BackupStore etc) (including backport-needed/*)?
The PR is at: fix: attempt to delete processes from instance-managers in unknown state (backport #3127) longhorn-manager#3154.
If labeled: require/automation-e2e Has the end-to-end test plan been merged? Have QAs agreed on the automation test case? If only test case skeleton w/o implementation, have you created an implementation issue (including backport-needed/*)
The automation skeleton PR is at: test: skeleton for don't orphan processes when node not ready longhorn-tests#2081.
The issue of automation test case implementation is at: [TEST][BUG] kubectl drain node is blocked by unexpected orphan engine processes #9375.

[BACKPORT][v1.6.3][BUG] kubectl drain node is blocked by unexpected orphan engine processes #9446