QFX5100 packet drop

Hi, Experts,

I found the QFX5100 interfaces xe-0/0/ has packet drop when connecting to a WAN link  ( oppsite partner = Cisco device, for our case).

But there is no packet drop when connecting to a LAN Link ( opposite partner = Cisco device,. also ).

Interfaces (MTU size is default)  in QFX5100 and Cisco device have no any error, like CRC, input/out, RUNT/Giant, unknown packet drop, unknown protocol drop... 

No QoS configuration in our devices ( Juniper and Cisco ).

Any advice for investigation of this problem (packet drop), thx so much for your kind help.