Just FYI the EX4200 Uplink Module command "set chassis fpc 0 pic 1 sfpplus pic-mode 1g/10g" is not applicable to EX4300 Uplink module; different implementation with this new hardware model.
The Uplink on EX4300 is still pic 1, but the sfpplus knob is no longer there, or needed. I would recommend not trying to mix 1GE SFP and 10GE SFP+ optics on EX4300 Uplink module as there maybe some hidden issues.
FYI and word to the wise.