I'm not sure which software is doing what here (maas or curtin), but it looks like something isn't generating that interfaces file properly.

For (3), one question is why is the hwaddress being specified in the interfaces file, given that the bond will inherit the address of its first slave (unless something sets it explicitly prior to the first slave being added)?

I'm wondering if there's a potential issue here if, e.g., the slave whose MAC is explicitly stated is later removed from the bond (editing the configuration file), the system rebooted, and then the bond and that slave would be configured with the same MAC.

Along the same lines, since "aliases" don't really exist as separate entities (they're just additional addresses on the actual interface with a special label for ifconfig backwards compatibility), there is no value in supplying the hwaddress at all.

Reportedly, the maas deployment fails intermittently.  The provided interfaces file produces a number of errors in syslog (most of these look to be from the bonding options in the alias sections):

Jun 2 11:36:19 ubuntu ifup[2667]: sh: echo: I/O error 
Jun 2 11:36:19 ubuntu kernel: [ 12.733066] bonding: no command found in bonding_masters - use +ifname or -ifname
Jun 2 11:36:19 ubuntu ifup[2667]: RTNETLINK answers: No such device 
Jun 2 11:36:19 ubuntu ifup[2667]: Cannot send link get request: No such device 
Jun 2 11:36:19 ubuntu ifup[2667]: /etc/network/if-pre-up.d/ifenslave: 65: /etc/network/if-pre-up.d/ifenslave: cannot create /sys/class/net/bond0:1/bonding/xmit_hash_policy: Directory nonexistent 
Jun 2 11:36:19 ubuntu ifup[2667]: /etc/network/if-pre-up.d/ifenslave: 65: /etc/network/if-pre-up.d/ifenslave: cannot create /sys/class/net/bond0:1/bonding/miimon: Directory nonexistent 
Jun 2 11:36:19 ubuntu ifup[2667]: RTNETLINK answers: No such device 
Jun 2 11:36:19 ubuntu ifup[2667]: Cannot send link get request: No such device 
Jun 2 11:36:19 ubuntu ifup[2667]: /etc/network/if-pre-up.d/ifenslave: 65: /etc/network/if-pre-up.d/ifenslave: cannot create /sys/class/net/bond0:1/bonding/mode: Directory nonexistent 
Jun 2 11:36:19 ubuntu ifup[2667]: RTNETLINK answers: No such device 
Jun 2 11:36:19 ubuntu ifup[2667]: Cannot send link get request: No such device 
Jun 2 11:36:19 ubuntu ifup[2667]: /etc/network/if-pre-up.d/ifenslave: 65: /etc/network/if-pre-up.d/ifenslave: cannot create /sys/class/net/bond0:1/bonding/lacp_rate: Directory nonexistent 
Jun 2 11:36:19 ubuntu ifup[2667]: Waiting for a slave to join bond0:1 (will timeout after 60s) 
Jun 2 11:36:19 ubuntu ifup[2667]: cat: '/sys/class/net/bond0:1/bonding/slaves': No such file or directory 
Jun 2 11:36:19 ubuntu ifup[2667]: message repeated 4 times: [ cat: '/sys/class/net/bond0:1/bonding/slaves': No such file or directory] 
Jun 2 11:36:20 ubuntu sh[3559]: Waiting for DAD... Done 
Jun 2 11:36:20 ubuntu ifup[2667]: cat: '/sys/class/net/bond0:1/bonding/slaves': No such file or directory 
Jun 2 11:36:20 ubuntu kernel: [ 13.832965] ixgbe 0000:04:00.0 eno1: NIC Link is Up 1 Gbps, Flow Control: RX/TX 
Jun 2 11:36:20 ubuntu kernel: [ 13.832999] IPv6: ADDRCONF(NETDEV_CHANGE): eno1: link becomes ready 
Jun 2 11:36:20 ubuntu kernel: [ 14.143160] ixgbe 0000:04:00.1 eno2: NIC Link is Up 1 Gbps, Flow Control: RX/TX 
Jun 2 11:36:20 ubuntu kernel: [ 14.143184] IPv6: ADDRCONF(NETDEV_CHANGE): eno2: link becomes ready 
Jun 2 11:36:56 ubuntu ifup[2667]: message repeated 355 times: [ cat: '/sys/class/net/bond0:1/bonding/slaves': No such file or directory] 
Jun 2 11:36:56 ubuntu systemd-timesyncd[2064]: Timed out waiting for reply from 91.189.89.199:123 (ntp.ubuntu.com). 
Jun 2 11:36:56 ubuntu ifup[2667]: cat: '/sys/class/net/bond0:1/bonding/slaves': No such file or directory 
Jun 2 11:37:06 ubuntu ifup[2667]: message repeated 101 times: [ cat: '/sys/class/net/bond0:1/bonding/slaves': No such file or directory] 
Jun 2 11:37:06 ubuntu systemd-timesyncd[2064]: Timed out waiting for reply from 91.189.94.4:123 (ntp.ubuntu.com). 
Jun 2 11:37:06 ubuntu ifup[2667]: cat: '/sys/class/net/bond0:1/bonding/slaves': No such file or directory 
Jun 2 11:37:20 ubuntu ifup[2667]: message repeated 136 times: [ cat: '/sys/class/net/bond0:1/bonding/slaves': No such file or directory] 
Jun 2 11:37:20 ubuntu ifup[2667]: No slave joined bond0:1, continuing anyway