Get_elem() getting called twice with CLI show command and with NETCONF its getting executed properly once

[cohult]

Another explanation:

Same callback is getting invoked for both get & set operation

Suggest not to use the CLI if you are looking for somewhat more predictable callback invocations. The CLI is a human-to-machine interface, so ConfD must fetch data for things like tab-complete, table look-ahead, etc. Use NETCONF or RESTCONF instead.

Your data provider application should not assume one callback invocation from ConfD per request.
If you want to support allocating an identifier, I suggest you use an action instead of an operational data provider.