On EX4650 and QFX5120-48Y, 10G interfaces are not coming up simultaneously when different Small Form-factor Pluggable (SFPs - 10G and 1G) are plugged in within the same 4 port group. Normally 10G interface by itself will be up when set to 1G if no other SFP is plugged in.

In a Quad group with SFP-10GBASE-T and SFP-LX, the SFP-LX interface will not be up when the speed is set to 1G. This issue is seen on platforms that have quad port restrictions and do not support 1G on a 10G interface. The presence of the SFP-10GBASE-T resets the speed of the port (with SFP-LX) to 10G (though configured to 1G).

{master:0}[edit]
user@ex4650# run show chassis hardware 
Hardware inventory:
Item             Version     Part number      Serial number   Description
Chassis                                       SN              JNP48Y8C-CHAS
Pseudo CB 0   
Routing Engine   0           BUILTIN          BUILTIN         RE-EX4650-48Y-8C
FPC 0            REV 15      650-083242       SN              JNP48Y8C-CHAS
 CPU                         BUILTIN          BUILTIN         FPC CPU
 PIC 0                       BUILTIN          BUILTIN         48x25G-8x100G
  Xcvr 16        REV 01      740-011614       SN              SFP-LX10       <<<<<<
  Xcvr 18        REV 01      740-083295       SN              10GBASE-T      <<<<<<

When quad is not configured to 1G speed only the xe (SFP-10GBASE-T) is coming up, while SFP-LX is not present:

{master:0}[edit]
user@ex4650# run show interfaces ge-0/0/16 terse   
error: device ge-0/0/16 not found

{master:0}[edit]
user@ex4650# run show interfaces xe-0/0/18 terse 
Interface        Admin Link Proto  Local         Remote
xe-0/0/18        up  up
xe-0/0/18.16386     up  up  

Configure the quad group for 1G speed:

{master:0}[edit]
user@ex4650# show chassis 
fpc 0 {
  pic 0 {
    port 16 {
      speed 1G;
    }
  }
}

The xe interface becomes ge and it shows as up, while ge-0/0/16 is recognized by the system but shows in down state:

{master:0}[edit]
user@ex4650> show interfaces terse   
Interface        Admin Link Proto  Local         Remote
ge-0/0/16         up  down
ge-0/0/16.16386   up  down
ge-0/0/18         up  up
ge-0/0/18.16386   up  up  

Remove the optic in port 18 (10GBASE-T transceiver), ge-0/0/16 then shows as Up:

{master:0}
user@ex4650> show interfaces terse   
Interface        Admin Link Proto  Local         Remote
ge-0/0/16        up    up
ge-0/0/16.16386  up    up  

There is no workaround or software fix as this is a hardware platform limitation. 

If you want to use SFP-10GBASE-T at 1G speed, use a separate quad of ports. Do not mix with other 1G SFPs because SFP-10GBASE-T deactivates other ports with a different 1G SFP module.

Public PR1714833 documents this hardware limitation.