How is Application Path Insights Statistics gathered

Latency

Jitter

Loss

For SSR Peer Path connections, BFD echo packet data is used to calculate the Latency, Jitter and loss Loss

https://www.juniper.net/documentation/us/en/software/session-smart-router/docs/howto_tune_bfd/#echo-mode

and

https://docs.128technology.com/docs/concepts_machine_communication/#bfd-path-quality