Hi lyndidon
Thank you for your comment, but I never mentioned 802.1ah or 802.1ad. The problem is that switch is dropping valid transit traffic and JTAC refuses to accept it as a problem. For better understanding please check PR1169654 (Q-in-Q Packets can not pass across QFX10000 configured as L2 transit device), it's very similar to my case.
I'm working in SP environment for more than 20 years and I met a lot of hardware/software bugs and most of them were successfully solved by vendors. But this is the first time when hardware vendor confirms the problem but claims that dropping valid ethernet frames is an expected behavior because switch is not designed to pass through valid ethernet frames with 3 vlan tags.
Best Regards
Michael Varyan