I have found that there are some interfaces which are going inactive on our SNMP polling and change detection is never bringing them back online. When you do a manual rediscover of that interface metric family, they come back. So far the only pattern I can see is that those interfaces are being updated by REST for speed overrides using this method: https://knowledge.broadcom.com/external/article?articleId=93510
Dx NetOps Performance Management 20.2
Dis-associate the collection that owns the devices from the monitoring profile, and then re-associate it. This will kick off a metric family discovery for devices in the collection and in this case, for interfaces, set them back to 'Active' status