Loraserver:get device-session error

I‘m testing ABP,from the server,I got the DEVADDR, APPSKEY,NWKSKEY after OTAA。I may have changed some configurations on the app-server. now,I saw the error on the loraserver log.I will provide any information you want.please help me,Thanks .

I am sure that my previous tests were normal, but I don’t know why this is happening now.