IPv6 unknown traffic under PPPoE or L2TP w/o 4G

Hi there
Using version 7.15.3 or 7.16.1 or 7.16.2, we get unexplained IPv6 trafic where source (and probably the router itself) is ::6501:0:0:0
Destination are real web server for example and for sure we can’t get any answer. Fact is we do consume bandwidth !
Any idea ?

We are using DHCPv6, bridging and no VRF at all

Thanks for your help

HI there,
same issue with 7.19.2 !