If you have the unit using a Mesh uplink (unknown if the issue happens with wired uplink, but I would suspect it would) and a Wired port set to the Default VLAN that port is passing Broadcast and Multicast traffic from ALL VLANS, not just VLAN 1 (the default).

A) This is a security issue as devices in isolated VLANs are able to use Broadcast or Multicast to send stuff to devices in the Default VLAN.

B) This causes issues with IPv6 because IPv6 RAs bleed over from other VLANs causing the devices to configure non-usable addresses on the interface, potentially breaking connectivity.

Apparently "Default" is similar to setting a port to be a member of All VLANs (i.e. send all VLANs) but just with a PVID of 1 (i.e. Incoming untagged is tagged/associated with said VLAN), which is TOTALLY inappropriate and stupid.

This does not happen on a port set to a specific VLAN.

Note, I cant even force set the VLAN to 1 because it errors out saying you cant set the VLAN to the same as the default.

It should also be noted this effects port ETH0 as well when not using it for an uplink, ofcourse it is unconfiguerble, but trying to use it for a client on the "Default" VLAN.

Also side note, in the Port configuration screen, when setting the VLAN, it calls the settings PVID, thats not exactly inline with industry nomenclature in this context. PVID would only be what incoming untagged packets are tagged/associated with, I suggest PVID be changed to "VLAN ID" or something similar.

And while dealing with this, another plea to allow configuering ETH0 on this device for a set VLAN in the first place.