Changing of WAN Interface not possible

[Maestro86]

I want to change DHCPv6 values in the WAN Interface to make IPv6 work (according to this document: https://wiki.opnsense.org/manual/how-tos/ipv6_dsl.html), but my browser tells me while applying the changes, that the connection has been reset. This occurs with every change i try to attempt with this interface.

I have OPNsense 19.7.8 on a Sophos SG330v1 Appliance. My WAN interface is PPPoE with DTAG.

[Maestro86]

The issue seems to be a bug. I have completely reinstalled OPNsense 19.7 on my appliance, updated it to 19.7.8 and only set up all interfaces (Because of the problem, I did not restore my config backup but configured everything manually). There is no plugin installed besides siproxd and igmpproxy. After some time (at least half an hour), I tried to change a setting within an interface and the error occured again. I uninstalled both plugins, restarted the box and again tried to change an interface setting, but the error is still present. I don´t see any weird in the logs.

A word to my interfaces: I have configured a LAGG interface with four ports and divided my LAN into three VLANs. One for LAN, one for VOIP and one for Management. My provider is DTAG, the WAN interface is VLAN 7 on one dedicated interface.

Can anyone check my findings to be sure, that it is not a coincidence?