It looks like you're trying to access the config datastore.

Could you try the following endpoint instead?

GET /rests/data/opendaylight-inventory:nodes?content=nonconfig 

Using content=nonconfig will retrieve data from the operational datastore.

You can find more examples in the official ODL documentation: https://docs.opendaylight.org/projects/openflowplugin/en/latest/users/operation.html