I have started getting the following error
Circular reference detected for service "domain.route_provider", path: "options_request_listener -> domain.route_provider -> cache_tags.invalidator -> config_ignore.event_subscriber -> config.storage.sync -> router -> router.no_access_checks"
when visiting a site after updating to 3.x, so config_ignore.event_subscriber looks to be the right place to break this loop.
Unfortunately I do not have a reliable way to reproduce it. It happens after clearing caches, but not on all pages. However it did not happen before the update, and regularly happens after it.
Load the config.storage.sync service right before it is used, not when config_ignore.event_subscriber service object is created.
Active
3.0
Code
#2 is causing errors during config export on this line:
$this->transformStorage($event->getStorage(), $this->syncStorage(), 'export');