NS device-session error

My network server log is full of the following error messages. How do I determine which device these uplinks are coming from. I would also welcome some advice on what causes this error condition.

chirpstack-network-server[477]: time=“2020-12-22T20:43:11+11:00” level=error msg=“uplink: processing uplink frame error” ctx_id=2328f8cf-fab9-48ca-b4b6-37ad417e3884 error=“get device-session error: object does not exist”

Thanks for any assistance.