Physical interface won't go up when added to Open vSwitch bridge

Recently I came across this Ask Ubuntu post about adding physical interfaces to an Open vSwitch bridge. The answers from Lukas Maerdian and Denis helped me a lot, but I still have one problem.

When I add the physical interface enp0s3 to the internal Open vSwitch port br-ex using the interfaces mapping inside the bridge br-ex, I can't get enp0s3 to reach the UP state during boot, I have to manually run ip link set enp0s3 up after the machine boots.

Here is my current Netplan configuration:

---
network:
  ethernets:
    enp0s3: {}
  bridges:
    br-ex:
      openvswitch: {}
      addresses:
        - 10.2.0.0/8
      gateway4: 10.0.0.1
      nameservers:
        addresses:
          - 10.0.0.1
      interfaces:
        - enp0s3
  version: 2
...

Here is my /var/log/syslog file with only the systemd-networkd lines (the whole file is huge).

Here is the stdout of ip addr:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp0s3: <BROADCAST,MULTICAST> mtu 1500 qdisc fq_codel master ovs-system state DOWN group default qlen 1000
    link/ether 08:00:27:9a:24:d8 brd ff:ff:ff:ff:ff:ff
3: ovs-system: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
    link/ether 7e:46:ed:8f:ae:cd brd ff:ff:ff:ff:ff:ff
4: br-int: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
    link/ether 82:69:1e:06:a2:42 brd ff:ff:ff:ff:ff:ff
5: br-ex: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000
    link/ether 08:00:27:9a:24:d8 brd ff:ff:ff:ff:ff:ff
    inet 10.2.0.0/8 brd 10.255.255.255 scope global br-ex
       valid_lft forever preferred_lft forever
    inet6 fe80::a00:27ff:fe9a:24d8/64 scope link
       valid_lft forever preferred_lft forever
6: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
    link/ether 52:54:00:c3:00:4b brd ff:ff:ff:ff:ff:ff
    inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
       valid_lft forever preferred_lft forever
7: virbr0-nic: <BROADCAST,MULTICAST> mtu 1500 qdisc fq_codel master virbr0 state DOWN group default qlen 1000
    link/ether 52:54:00:c3:00:4b brd ff:ff:ff:ff:ff:ff

ovs-vsctl show gives me:

6a9ff04c-316f-4ee8-82e1-f228c512cf74
    Manager "ptcp:6640:127.0.0.1"
        is_connected: true
    Bridge br-int
        fail_mode: secure
        Port br-int
            Interface br-int
                type: internal
        Port patch-br-int-to-provnet-8d56ff0f-c67a-4219-8cfc-bcf8aa009f28
            Interface patch-br-int-to-provnet-8d56ff0f-c67a-4219-8cfc-bcf8aa009f28
                type: patch
                options: {peer=patch-provnet-8d56ff0f-c67a-4219-8cfc-bcf8aa009f28-to-br-int}
    Bridge br-ex
        fail_mode: standalone
        Port patch-provnet-8d56ff0f-c67a-4219-8cfc-bcf8aa009f28-to-br-int
            Interface patch-provnet-8d56ff0f-c67a-4219-8cfc-bcf8aa009f28-to-br-int
                type: patch
                options: {peer=patch-br-int-to-provnet-8d56ff0f-c67a-4219-8cfc-bcf8aa009f28}
        Port enp0s3
            Interface enp0s3
        Port br-ex
            Interface br-ex
                type: internal
    ovs_version: "2.13.3"

I need enp0s3 to automatically go up when the machine boots, but I can't figure out how to do so. Without adding enp0s3 as an interface to br-ex, enp0s3 goes up during boot normally.