The pps and bps rate may become zero after removing one of VCP ports from QFX5k which is working on virtual-chassis. There is no traffic loss but you cannot check proper value of pps and bps rate by CLI command.
The issue is seen when QFX is receiving traffic with IEEE802.1Q CoS value other than default value 1 and passing through VCP ports. This is a software issue which already have a fix.

Here is the sample output, before observing the issue, pps and bps rate on egress xe-1/0/32 was incremented.
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Interface    Link  Input packets        (pps)     Output packets        (pps)
vcp-255/0/24  Up          19500         (27)            23955         (32)
vcp-255/0/25  Up           1733          (1)           935880       (1001)
vcp-255/0/26  Up            796          (0)              810          (0)
vcp-255/0/27  Up            802          (0)              813          (0)
~snip~
xe-1/0/32     Up            952          (0)           935671       (1001)  <<<====== Seeing pps output
ae1           Up         934905       (1000)              971          (1)
ae3           Up            952          (0)           935671       (1001)  <<<====== Seeing pps output
--------------------

user@Switch# run show interfaces xe-1/0/32 extensive
Physical interface: xe-1/0/32, Enabled, Physical link is Up
~snip~
  Statistics last cleared: Never
  Traffic statistics:
   Input  bytes  :               602412                  664 bps
   Output bytes  :            885297784               801256 bps  <<<=============== Seeing bps output
   Input  packets:                 8859                    1 pps
   Output packets:              8850513                 1001 pps  <<<=============== Seeing pps output

--------------------

After removing one of VCP ports, pps and bps rate on egress xe-1/0/32 was not incremented.

--------------------
Interface    Link  Input packets        (pps)     Output packets        (pps)
 vcp-255/0/24Down          20256          (0)            24780          (0)  <<<====== Down
 vcp-255/0/25  Up           2469         (32)           965481         (27)
 vcp-255/0/26  Up            859          (1)              856          (0)
 vcp-255/0/27  Up            846          (0)            24358        (999)
~snip~
 xe-1/0/32     Up           1004          (0)           987806          (1)  <<<====== No pps output
 ae1           Up         987153       (1000)             1024          (1)
 ae3           Up           1004          (0)           987806          (1)  <<<====== No pps output
--------------------

user@Switch# run show interfaces xe-1/0/32 extensive
Physical interface: xe-1/0/32, Enabled, Physical link is Up
~snip~
  Statistics last cleared: Never
  Traffic statistics:
   Input  bytes  :               614652                  328 bps
   Output bytes  :            903326424                 1248 bps  <<<=============== This is less than flowing bps rate while stats is incrementing
   Input  packets:                 9039                    0 pps
   Output packets:              9030749                    1 pps  <<<=============== No pps output while stats is incrementing
   IPv6 transit statistics:
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