After doing that, MAAS should recommission the machine to gather the new networking information and then saving this to the database. You mentioned that you can see in the Controllers->Interfaces tab that the bridge is recognized but does it appear to be on the correct VLAN?
Nicolas,
Thanks for reporting this. Did you try restarting the MAAS services after running netplan apply?
$ sudo systemctl restart maas-regiond && sudo systemctl restart maas-rackd
After doing that, MAAS should recommission the machine to gather the new networking information and then saving this to the database. You mentioned that you can see in the Controllers- >Interfaces tab that the bridge is recognized but does it appear to be on the correct VLAN?