Hello
There could be a number of reasons:
https://forums.juniper.net/t5/SRX-Services-Gateway/DUP-ping-response/td-p/164474
https://forums.freebsd.org/threads/dup-in-ping-replies-to-or-from-server.36371/
BR,
Andrei
Accept as Solution = cool !
Accept as Solution+Kudo = You are a Star !