The managed OPA instances are automatically configured to export Prometheus metrics. See operators:monitoring.adoc for more details.
You can read on the list of exported metrics in the OPA monitoring documentation.
Especially worth mentioning are the Status metrics, which contain e.g. opa_info, bundle_loaded_counter and bundle_failed_load_counter.
You can use those to create a Dashboard to quickly see any bundle loading problems.
Additionally, you can use set up an alert based on this, so that you are proactively informed.