Cant save WAN DHCPv6 settings

[wuast94]

I try to enable dhcpv6 on my network, when i change settings on my WAN interface and hit save it loads some time and shows me an ERR_CONNECTION_RESET

when i reload the page all changes are gone

i even cant enable the dhcpdv6 on the dashboard

didnt find anything with google on this problem, hope someone here has a hint :)