Assuming Netflix used its extensive edge cache network to distribute the streams to the ISPs. The software on the caching servers would have been updated to be capable of dealing with receiving and distributing live streamed content, even if maybe the hardware was not optimal for that (throughput vs latency is a classic networking tradeoff).
Now inside the ISPs network again everyting would probably be optimized for the 99.99% usecase of the Netflix infra: delivering large bulk data that is not time sensitive. This means very large buffers to shift big gobs of packets in bulk.
As everything along the path is trying to fill up those buffers before shipping to the next router on the path, some endpoints aware this is a live stream start cancelling and asking for more recent frames ...
Hilarity ensues