VIAVI TestCenter - Automation: REST-API failed to join session getting error: Failed to join session "SIT_STAR - CE"

Using 4.77 to running a cafy script (restful API), below “connection refuse” happened on the script with multiple running. -Info-----2019-09-20T11-09-29[MainThread][spirent]> sid is SIT_STAR - CE -Error----2019-09-20T11-09-29[MainThread][star_utils]> Error while connecting to existing Spirent session. Retry 3.. Error: Failed to join session "SIT_STAR - CE":500 INTERNAL SERVER ERROR: server error: [Errno 111] Connection refused Traceback (most recent call last): File "/auto/lindt-paragon/SIT-STAR/cafykit/lib/tgn/spirent.py", line 523, in _join_session ['version', 'name']) File "/auto/lindt-paragon/SIT-STAR/cafykit/lib/tgn/spirent_resthttp.py", line 224, in get_request return self._handle_response(rsp, to_lower) File "/auto/lindt-paragon/SIT-STAR/cafykit/lib/tgn/spirent_resthttp.py", line 459, in _handle_response raise RestHttpError(rsp.status_code, rsp.reason, detail, code) tgn.spirent_resthttp.RestHttpError: 500 INTERNAL SERVER ERROR: server error: [Errno 111] Connection refused   During handling of the above exception, another exception occurred: Traceback (most recent call last): File "/auto/lindt-paragon/SIT-STAR/star/star/infra/utils.py", line 1978, in connect_to_tgen_session tgen_device.connect_to_session(session_name) File "/auto/lindt-paragon/SIT-STAR/cafykit/lib/tgn/spirent.py", line 1338, in connect_to_session self._join_session(self._sid) File "/auto/lindt-paragon/SIT-STAR/cafykit/lib/tgn/spirent.py", line 527, in _join_session raise CafyException.TgenClientError('Failed to join session "%s":'%(sid) + str(e)) utils.cafyexception.CafyException.TgenClientError: Failed to join session "SIT_STAR - CE":500 INTERNAL SERVER ERROR: server error: [Errno 111] Connection refused -Fail-----2019-09-20T11-09-29[MainThread][star_tc_base]> Exception during VerifyTraffic oper -Error----2019-09-20T11-09-29[MainThread][star_tc_base]> Error: Error while connecting to existing Spirent session after 3 tries. Traceback (most recent call last): File "/auto/lindt-paragon/SIT-STAR/star/star/infra/tc_base.py", line 478, in execute_oper result = oper.execute() File "/auto/lindt-paragon/SIT-STAR/star/star/operations/verifications/verify_traffic.py", line 76, in execute connect_to_tgen_session(self.tgn_device, self.param.session_name) File "/auto/lindt-paragon/SIT-STAR/star/star/infra/utils.py", line 1983, in connect_to_tgen_session raise Exception("Error while connecting to existing Spirent session after 3 tries.") Exception: Error while connecting to existing Spirent session after 3 tries. -Info-----2019-09-20T11-09-29[MainThread][star_tc_base]> Oper: VerifyTraffic : EXCEPTION  

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