When you have 4x10GbE SFP+ extension module (EX4400-EM-4S) on EX4400 with 1G SFP, and configure chassis fpc 0 pic 2 port 0 speed 1g, the 1g SFP port will only come up when you use no-auto-negotiation.

When turning on auto-negotiation, EX4400 ports are shown up, but the peering end ports might show as down.

Auto-Negotiation is not supported in PIC1/PIC2 on EX4400.

Disable auto-negotiation to bring up the interface.