A bucket which at some time had a few objects in infrequent access storage still shows in the metrics view some usage of infrequent storage even though those objects have been deleted long ago. The non-existent objects also get billed.
April 20th or earlier according to the audit log (which doesn't show individual deletes). But even then the metrics shouldn't still show these objects if they are not there anymore. Or is there some hidden option to make stale objects visible?