When you have a bridge with two interfaces in my case it was an openvpn layer 2 tunnel and a vif vlan interface (like ethX.10).
Then when we edit the configuration from the parent interface (ethX) like by adding a new vlan (ethX.11) the ethX.10 gets removed from the bridge.
To reproduce
set interfaces ethernet eth1 vif 100 set interfaces bridge br1 member interface eth1.100 commit set interfaces ethernet eth1 vif 200 commit
Interface/bridge status
vyos@r5-roll# run show int Codes: S - State, L - Link, u - Up, D - Down, A - Admin Down Interface IP Address S/L Description --------- ---------- --- ----------- br1 - A/D eth0 192.168.122.15/24 u/u eth1 - u/u eth1.100 - u/u eth1.200 - u/u vyos@r5-roll# sudo brctl show bridge name bridge id STP enabled interfaces br1 8000.000000000000 no [edit] vyos@r5-roll#