Second Ethereum RPC metrics are not tracked

Do you want to request a feature or report a bug?
Bug

What is the current behavior?
When adding a second Ethereum RPC, we lose visibility in Grafana of the time for eth_getLogs calls - deployment_eth_rpc_request_duration. This was done recently for the matic network on the Hosted Service.

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem.
Add two Ethereum RPCs, the second of which should be a non-archive node (so it is used for eth_getLogs calls). The deployment_eth_rpc_request_duration is no longer tracked. eth_call duration will be tracked (as those hit the archive URL)

Hypothesis: possibly graph node tries to register the same metric twice, one for each url, which is an error

What is the expected behavior?
Metrics should be tracked for all nodes - ideally we should also be able to distinguish metrics by node?

The issue names no files or tests. Start by reproducing the setup with two Ethereum RPCs, then trace registration and collection of deployment_eth_rpc_request_duration for eth_getLogs and eth_call. Done means request-duration metrics remain available for every configured node, ideally distinguishable by node.