[ML] Errors logged ML:saved-objects-sync-task:task

[sophiec20]

Kibana version:
9.1

Describe the bug:
Increased error logging shows possible race condition in task claiming where it seems the task was temporarily unavailable- this can trigger false-positive alerts.

{"type":"document_missing_exception",
"reason":"[task:ML:saved-objects-sync-task]: document missing",
"index_uuid":"5ZNoavROR6yW-YyrQBMOCw","shard":"0",
"index":".kibana_task_manager_1"}

Error getting full task ML:saved-objects-sync-task:task during claim: 
Saved object [task/ML:saved-objects-sync-task] not found

Related

• No need to remove a task #226481

Expected behavior:
Reduction in spurious error logs

APEX-94

[elasticmachine]

Pinging @elastic/ml-ui (:ml)