Issue with queue tree stop working

Hi all,

I use queue trees for VoIP QoS (routerOS v7.6). SIP/RTP packet & connections are correctly marked with mangle.

But sometimes one of the queue tree child see some packets then stop working, the packet/bytes counters stay fixed.
Then if I delete and recreate the queue tree child with exactly same config, it works again and counters are correctly incremented like mangle.

Is there a bug somewhere in queue trees ?

Regards