Infrastructure monitoring will tell you the edge is healthy and the origin is responding. It cannot tell you that viewers on one mobile network are rebuffering every ninety seconds, because from the server's side every one of those requests succeeded.
There is a gap between "the system is up" and "it is watchable", and almost everything you can measure on a server sits on the wrong side of it.
A rebuffer is a client-side event. The player ran out of buffered media and stopped. From the edge's perspective the segment requests around that moment all returned 200 in reasonable time — because they did. The failure is in the relationship between arrival rate and playback rate, and only one end of that relationship is on your infrastructure.
Every player — web, phone, television — reports per session:
Sliceable by network, device, region and title, because the finding is almost never global. It is one carrier, or one device generation, or one title with a bad ladder.
Per-session licensing prices exactly the thing you are trying to grow. But the stronger argument is that the data is your viewers' behaviour, held in your own estate, with retention you set — and there is no third-party processor to declare in a privacy assessment.
Turning this on will surface problems that already existed. That is the point, and it is still unpleasant: the graph does not distinguish between "we made it worse" and "we can finally see it". Worth deciding in advance who owns the number, before the first bad week makes it a debate.
If the pattern in this write-up describes your setup, the next step is reading your actual numbers against it. Send twelve months of billing and your concurrency curve.