You can fix this by updating the REST host created by the workflow(s). Browse to the catalog view in the vRO interface, then expand the HTTP-REST tree and find the one named "Stored WFA Host".
Right click on the host and select "Run Workflow". In the popup, select "Update a REST Host". Make sure you choose the one at the path "Library / HTTP-REST / ...".
After the workflow starts, go to step 1b and choose "Yes" for the question "If set to true, the certificate is accepted silently..."
Next, go to step 3a, answer the question with "No", then click Submit on the workflow.
Once it's done, test your workflow again to see if the error has gone away.
Hope that helps.
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