Receiving below error while saving the flow. I have not seen such an error prior. Any suggestions about in what case this could happen?

The error log shows it is complaining about a cyclical reference.

2020-06-05 16:18:12,866 INFO [default] [Agile Requirements Designer Hub Log]ReturnedMessage: {"timestamp":"2020-06-05T20:18:12.857+0000","status":422,"error":"Unprocessable Entity","message":"The following subflows cause a cyclic reference:\n\"TS411 New TFNs, HFP, No CCD, No Expediate on new H4 and H6 with one site\"","path":"/ard/flow-storage/v1/flows/1c799e66-ffc4-4391-aa4d-276fe8c5723a"}

Can you check the flow: TS411 New TFNs, HFP, No CCD, No Expediate on new H4 and H6 with one site
and check its subflows and references.
Can you also check the subflow links to this subflow from TS405 TN TFN Install TN Manual Order Reject TNs Partial?

Release : 3.0

Component : CA Agile Requirements Designer

Deleting the cyclic reference corrected the issue.