Any idea ? or its normal ?
I'm not sure, but I also saw this for the first time today after enabling ipv6 on a relay last week. A quick look at the relevant code doesn't shed any immediate light on what would be causing this (the triggering request is to establish a rendezvous point with a hidden service, but I'm not familiar with the semantics of the CIRCUIT_PURPOSE check that's failing).
Relevant: https://trac.torproject.org/projects/tor/ticket/15618
Regards, Sharif