Got Same issue and it is a published Workflow. Had saved it and tried to open again, then I got the same error message.
I had made changes to the Workflow and saved it, closed it. Then when I tried to open it again, it gave the below error. The Workflow has been published before. I don't have a backup and there are around 73 actions in it. Really need help on this.
See the attached PDF for instructions on how to try fix this error.
Note that this is a last resort method. Attempt at your own risk.
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