Automation:It always raise an error"Lost network connection to the server; please reconnect again." as i create relations between the interface under device

I want to create relations between pppoeif and ethiiif or between pppif and pppoeif

Error like this:

stcrestclient.resthttp.RestHttpError: 500 Internal Server Error: STC exception: in apply: Lost network connection to the server; please reconnect again.