NetworkManager managed devices continuously flap causing outages

Issue

• In some cases, MTU changes from 9000 to 1500 constantly
• Seeing messages in the logs similar to those below:

Aug  7 14:58:11 localhost kernel: ixgbe 0000:0c:00.0 enp12s0: changing MTU from 9000 to 1500
Aug  7 14:58:57 localhost kernel: ixgbe 0000:0c:00.0 enp12s0: changing MTU from 9000 to 1500
Aug  7 14:59:47 localhost kernel: ixgbe 0000:0c:00.0 enp12s0: changing MTU from 9000 to 1500
Aug  7 14:59:55 localhost kernel: ixgbe 0000:0c:00.0 enp12s0: changing MTU from 9000 to 1500

• The links are constantly flapping and NetworkManager is trying to assign an IP address to the device and failing:

$ grep NetworkManager sos_commands/logs/journalctl_--no-pager_--catalog_--boot | egrep "bond0|bond1" | grep "ip-config -> failed" | head
Jun 16 16:56:06 hostname.example.com NetworkManager[3633]: <info>  [1623842766.0275] device (bond1): state change: ip-config -> failed (reason 'ip-config-unavailable', sys-iface-state: 'managed')
Jun 16 16:56:07 hostname.example.com NetworkManager[3633]: <info>  [1623842767.0262] device (bond0): state change: ip-config -> failed (reason 'ip-config-unavailable', sys-iface-state: 'managed')
Jun 16 16:56:55 hostname.example.com NetworkManager[3633]: <info>  [1623842815.0273] device (bond1): state change: ip-config -> failed (reason 'ip-config-unavailable', sys-iface-state: 'managed')
Jun 16 16:56:55 hostname.example.com NetworkManager[3633]: <info>  [1623842815.4855] device (bond0): state change: ip-config -> failed (reason 'ip-config-unavailable', sys-iface-state: 'managed')
Jun 16 16:57:43 hostname.example.com NetworkManager[3633]: <info>  [1623842863.0269] device (bond1): state change: ip-config -> failed (reason 'ip-config-unavailable', sys-iface-state: 'managed')
Jun 16 16:57:44 hostname.example.com NetworkManager[3633]: <info>  [1623842864.0264] device (bond0): state change: ip-config -> failed (reason 'ip-config-unavailable', sys-iface-state: 'managed')
Jun 16 16:58:31 hostname.example.com NetworkManager[3633]: <info>  [1623842911.0268] device (bond1): state change: ip-config -> failed (reason 'ip-config-unavailable', sys-iface-state: 'managed')
Jun 16 16:58:31 hostname.example.com NetworkManager[3633]: <info>  [1623842911.4898] device (bond0): state change: ip-config -> failed (reason 'ip-config-unavailable', sys-iface-state: 'managed')
Jun 16 17:04:18 hostname.example.com NetworkManager[3633]: <info>  [1623843258.0265] device (bond0): state change: ip-config -> failed (reason 'ip-config-unavailable', sys-iface-state: 'managed')
Jun 16 17:04:18 hostname.example.com NetworkManager[3633]: <info>  [1623843258.4778] device (bond1): state change: ip-config -> failed (reason 'ip-config-unavailable', sys-iface-state: 'managed')

• The links are configured with a static IP address, but NetworkManager TRACE level logs show that NetworkManager is reaching timeouts for IPv6 autoconf:

Apr 23 10:48:51 hostname.example.com NetworkManager[554471]: <debug> [1713865731.1481] device[xxxxxxxxxxxxxxxx] (eth1): ip:ac6: timeout for autoconf (IPv6 router advertisement) reached
Apr 23 10:48:51 hostname.example.com NetworkManager[554471]: <debug> [1713865731.1483] device[xxxxxxxxxxxxxxxx] (eth1): ip:ac6: set state: fail (was pending)
Apr 23 10:48:51 hostname.example.com NetworkManager[554471]: <trace> [1713865731.1487] device[xxxxxxxxxxxxxxxx] (eth1): ip6: check-state: state pending => fail, is_failed=1, is_pending=0, is_started=1 temp_na=0, may-fail-4=1, may-fail-6=1; 
disabled4; manualip4=done; manualip6=done ll6=done ac6=fail
Apr 23 10:48:51 hostname.example.com NetworkManager[554471]: <debug> [1713865731.1487] device[xxxxxxxxxxxxxxxx] (eth1): ip6: set state fail (was pending, reason: check-ip-state)
Apr 23 10:48:51 hostname.example.com NetworkManager[554471]: <trace> [1713865731.1487] device[xxxxxxxxxxxxxxxx] (eth1): ip: check-state: (combined) state pending => fail
Apr 23 10:48:51 hostname.example.com NetworkManager[554471]: <debug> [1713865731.1488] device[xxxxxxxxxxxxxxxx] (eth1): ip: set (combined) state fail (was pending, reason: check-ip-state)