Device is not showing

Devices are not showing some time .
Please explain it is inportant .
Aws Ram is 8 GB so i am sure it is not a problem of aws.

@brocaar @bconway
i got message error undeined.
undefined (code undefined).

i am also facing same issue, approximately 2 to 3 times in a day. once restart the AS server am able to see the devices. AS server is deployed in Azure Kubernetes.
please help me out.
thanks in advance.