Hello,
If You follow this KB, there is a bit of configuration missing, namely, static ARP on port-mirror output interface.
For the KB example config, it would be
set interfaces ge-0/0/1.0 family inet address 2.2.2.1/24 arp 2.2.2.2. mac 0e:00:00:00:00:0e
Please add static ARP entry to Your config, re-test and report back.
HTH
Thx
Alex