an inside LAN machine establish a V4tunnel with a internet provider to have an IPV6 address, the connection establish, ipv6 address is valid.
after a while (long while, few days maybe) the IPV6 tunnel becomes dumb.
no more ping -6 to any ipv6 address. At this time it is impossible to bring up the tunnel again, except if I go to mikrotik router and kill the existing connection, the only one of type 41 in the connection list. after killing the connection, tunnel is able to bring up again.
… filling in a bug report.