Hi @Alice01 ,
Is there anything has been changed before the issue occurs?
You could try the following steps:
1.Remove the checkout required from the library. However this isn’t the best solution because there is likely business reasons why you needed it enabled in the first place.
2.Add a step in the workflow to check out the document before you do anything and in the final step (no matter the outcome of the workflow) check it back in.
For Reference:
Another Cause of a SharePoint Workflow Stuck at Starting or Started
If your SP2010 Workflows are stuck in the Starting state
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