Metrics shown as being retrieved but can't be queried

Here's how I run the stackdriver_exporter with debug output:

./stackdriver_exporter --log.level=debug --google.project-ids=my-project --monitoring.metrics-prefixes='networking.googleapis.com/cloud_netslo' --monitoring.drop-delegated-projects --monitoring.filters='networking.googleapis.com/cloud_netslo'
time=2025-05-06T19:25:52.778Z level=INFO source=stackdriver_exporter.go:366 msg="Starting stackdriver_exporter" version="(version=0.18.0, branch=HEAD, revision=3b1a6e9ebb85a176b8ab48639f8e0a2a4a2f7bcf)" build_context="(go=go1.23.5, platform=linux/amd64, user=root@34d306216a55, date=20250117-20:46:30, tags=unknown)" metric_prefixes=[networking.googleapis.com/cloud_netslo] extra_filters=networking.googleapis.com/cloud_netslo projectIDs=[my-project] projectsFilter=""
time=2025-05-06T19:25:52.778Z level=INFO source=stackdriver_exporter.go:219 msg="Creating collector cache" ttl=2h0m0s
time=2025-05-06T19:25:52.778Z level=INFO source=tls_config.go:347 msg="Listening on" address=[::]:9255
time=2025-05-06T19:25:52.778Z level=INFO source=tls_config.go:350 msg="TLS is disabled." http2=false address=[::]:9255
time=2025-05-06T19:26:01.579Z level=DEBUG source=monitoring_collector.go:383 msg="listing Google Stackdriver Monitoring metric descriptors starting with" project_id=my-project prefix=networking.googleapis.com/cloud_netslo
time=2025-05-06T19:26:01.844Z level=DEBUG source=monitoring_collector.go:285 msg="retrieving Google Stackdriver Monitoring metrics for descriptor" project_id=my-project descriptor=networking.googleapis.com/cloud_netslo/active_probing/probe_count
time=2025-05-06T19:26:01.844Z level=DEBUG source=monitoring_collector.go:315 msg="retrieving Google Stackdriver Monitoring metrics with filter" project_id=my-project filter="project="my-project" AND metric.type="networking.googleapis.com/cloud_netslo/active_probing/probe_count""
time=2025-05-06T19:26:02.071Z level=DEBUG source=monitoring_collector.go:398 msg="Done reporting monitoring metrics" project_id=my-project
time=2025-05-06T19:30:18.083Z level=DEBUG source=monitoring_collector.go:383 msg="listing Google Stackdriver Monitoring metric descriptors starting with" project_id=my-project prefix=networking.googleapis.com/cloud_netslo
time=2025-05-06T19:30:18.148Z level=DEBUG source=monitoring_collector.go:285 msg="retrieving Google Stackdriver Monitoring metrics for descriptor" project_id=my-project descriptor=networking.googleapis.com/cloud_netslo/active_probing/probe_count
time=2025-05-06T19:30:18.148Z level=DEBUG source=monitoring_collector.go:315 msg="retrieving Google Stackdriver Monitoring metrics with filter" project_id=my-project filter="project="my-project" AND metric.type="networking.googleapis.com/cloud_netslo/active_probing/probe_count""
time=2025-05-06T19:30:18.360Z level=DEBUG source=monitoring_collector.go:398 msg="Done reporting monitoring metrics" project_id=my-project
time=2025-05-06T19:31:07.423Z level=DEBUG source=monitoring_collector.go:383 msg="listing Google Stackdriver Monitoring metric descriptors starting with" project_id=my-project prefix=networking.googleapis.com/cloud_netslo
time=2025-05-06T19:31:07.468Z level=DEBUG source=monitoring_collector.go:285 msg="retrieving Google Stackdriver Monitoring metrics for descriptor" project_id=my-project descriptor=networking.googleapis.com/cloud_netslo/active_probing/probe_count
time=2025-05-06T19:31:07.468Z level=DEBUG source=monitoring_collector.go:315 msg="retrieving Google Stackdriver Monitoring metrics with filter" project_id=my-project filter="project="my-project" AND metric.type="networking.googleapis.com/cloud_netslo/active_probing/probe_count""
time=2025-05-06T19:31:07.682Z level=DEBUG source=monitoring_collector.go:398 msg="Done reporting monitoring metrics" project_id=my-project

Despite the fact that the required metrics (cloud_netslo/active_probing/probe_count) are claimed to be retrieved from GCM as shown in the debug output, they do not appear on the list when '/metrics' is queried, and cannot be retrieved.

Start by reproducing the shown exporter command and query the /metrics endpoint. Trace the descriptor and metric retrieval flow in monitoring_collector.go, focusing on the logged lines around 285, 315, 383, and 398. Done means the cloud_netslo/active_probing/probe_count metric is exposed and retrievable from /metrics.