After committing config for a new 10G lane on a 4x10G breakout optic and connecting the cable to the machine, the forwarding towards the other two lanes on the same optic was broken.

The PTX10003 is not sending out any more traffic on these lanes.

The protocols go down, as the ping drops & interface can be seen staying up.
 

labroot@jtac-ptx10003-160c-r2003> ping 10.10.10.1    
PING 10.10.10.1 (10.10.10.1) 56(84) bytes of data.
64 bytes from 10.10.10.1: icmp_seq=16 ttl=64 time=1020 ms
64 bytes from 10.10.10.1: icmp_seq=17 ttl=64 time=0.741 ms
64 bytes from 10.10.10.1: icmp_seq=18 ttl=64 time=1.07 ms

labroot@jtac-ptx10003-160c-r2003> configure 
Entering configuration mode

[edit]
labroot@jtac-ptx10003-160c-r2003# delete interfaces et-0/1/8:3 

[edit]
labroot@jtac-ptx10003-160c-r2003# commit 
commit complete

[edit]
labroot@jtac-ptx10003-160c-r2003# exit 
Exiting configuration mode

labroot@jtac-ptx10003-160c-r2003> ping 10.10.10.1    
PING 10.10.10.1 (10.10.10.1) 56(84) bytes of data.
^C
--- 10.10.10.1 ping statistics ---
360 packets transmitted, 0 received, 100% packet loss, time 367603ms

Issue was replicated in lab & PR1810718 was raised & resolved via PR.
 

RCA:
When MTU/VLAN configs of 3 channel of 4x10GE or 4x25GE interface is modified when neighbour port is 400GE interface (provided 400GE interface is created post 4x10GE/4x25GE creation), packet drops are seen on all 4x10GE and 4x25GE interface.

Workaroud:

Following steps shall be performed to fix the issue as workaround,
1. Deactivate all interface configurations on all channelized interfaces et-x/y/z:[0..3]
2. Activate all interface configurations on all channelized interfaces et-x/y/z:[0..3]
Deactivate causes all channelized interfaces to get configured with default configurations.
Activate causes all configurations to get loaded on channelized interfaces. Activate causes IFD's to get deleted and recreated.