To echo Alain's comments earlier, the Juniper QFX 5100 series is stable, once you figure out all the shortcomings of the chipset.  We aren't doing anything fancy, but have certainly bumped into our share of issues that have no workaround because it's a limitation of the physical hardware.  Since we're talking about counters, see if you can spot the error with IPv6 accounting in the output from our 5100 below (about 50% of our traffic is v6):

    Transit statistics:
     Input  bytes  :      284315487788005            412457312 bps
     Output bytes  :       39937401090441             29417528 bps
     Input  packets:         231391925059                39552 pps
     Output packets:          88278182551                10809 pps
     IPv6 transit statistics:
      Input  bytes  :                   0
      Output bytes  :                   0
      Input  packets:                   0
      Output packets:                   0


;-)

I believe the 5100 just announced EOL (https://support.juniper.net/support/eol/product/qfx_series/); I haven't had time to look at the replacement models to see if they behave any better.

Jason