keepalived doesn't detect loss of virtual IP

I'm using keepalived to switch a floating IP between two VMs.

/etc/keepalived/keepalived.conf on VM 1:

vrrp_instance VI_1 {
    state MASTER
    interface ens160
    virtual_router_id 101
    priority 150
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass secret
    }
    virtual_ipaddress {
        1.2.3.4
    }
}

/etc/keepalived/keepalived.conf on VM 2:

vrrp_instance VI_1 {
    state MASTER
    interface ens160
    virtual_router_id 101
    priority 100
    advert_int 1
    authentication {
        auth_type PASS
        auth_pass secret
    }
    virtual_ipaddress {
        1.2.3.4
    }
}

This basically works fine, with one exception: Everytime systemd gets updated (it's running Ubuntu 18.04) it reloads it's network component, resulting in dropping the floating IP because it's not configured in the system. Since both keepalived instances still can ping each other, none of them sees anything wrong and none of them reacts on this, resulting in the floating IP staying down.

I found that you can check for the IP with a simple script like this:

vrrp_script chk_proxyip {
    script "/sbin/ip addr |/bin/grep 1.2.3.4"
}

vrrp_instance VI_1 {
    # [...]
    track_script {
        chk_proxyip
    }
}

But I'm not sure if this is a working approach.

If I understand it correctly the following would happen, if I configure this script on VM1:

1. VM1 loses the IP due to a systemd restart
2. keepalived on VM1 detects the loss of the IP
3. keepalived switches to FAULT state and stops broadcasting vrrp packages
4. keepalived on VM2 detects the loss of keepalived on VM1 and puts the floating IP up

At this point the IP is working again on VM2, but VM1 would stay in this state because the IP never comes up again on VM1. If VM2 goes down (for whatever reason) VM1 wouldn't take it over, because it is still in FAULT state.

How can I ensure that the floating IP is always up on one of the VMs?

Further tests:

I tried to ping the floating IP instead of checking if it is active on a specific host in a check_script:

vrrp_script chk_proxyip {
    script "/bin/ping -c 1 -w 1 1.2.3.4"
    interval 2
}

Configuring this script on node 2 resulted in the following:

1. removed the IP on node 1 for testing
2. node 2 detected the IP loss and changed from BACKUP to FAULT
3. node 1 ignored the state change and stayed MASTER

The result: the IP stayed down.

Configuring the script on node 1 resulted in the following:

1. removed the IP on node 1
2. node 1 detected the IP loss and changed from MASTER to FAULT
3. node 2 detected the state change on node 1 and changed from BACKUP to MASTER, configuring the floating IP on node 2

Well, and then ...

Feb 13 10:11:26 node2 Keepalived_vrrp[3486]: VRRP_Instance(VI_1) Transition to MASTER STATE
Feb 13 10:11:27 node2 Keepalived_vrrp[3486]: VRRP_Instance(VI_1) Entering MASTER STATE
Feb 13 10:11:29 node2 Keepalived_vrrp[3486]: VRRP_Instance(VI_1) Received advert with higher priority 150, ours 100
Feb 13 10:11:29 node2 Keepalived_vrrp[3486]: VRRP_Instance(VI_1) Entering BACKUP STATE
Feb 13 10:11:32 node2 Keepalived_vrrp[3486]: VRRP_Instance(VI_1) Transition to MASTER STATE
Feb 13 10:11:33 node2 Keepalived_vrrp[3486]: VRRP_Instance(VI_1) Entering MASTER STATE
Feb 13 10:11:36 node2 Keepalived_vrrp[3486]: VRRP_Instance(VI_1) Received advert with higher priority 150, ours 100
Feb 13 10:11:36 node2 Keepalived_vrrp[3486]: VRRP_Instance(VI_1) Entering BACKUP STATE
Feb 13 10:11:38 node2 Keepalived_vrrp[3486]: VRRP_Instance(VI_1) Transition to MASTER STATE
Feb 13 10:11:39 node2 Keepalived_vrrp[3486]: VRRP_Instance(VI_1) Entering MASTER STATE
Feb 13 10:11:41 node2 Keepalived_vrrp[3486]: VRRP_Instance(VI_1) Received advert with higher priority 150, ours 100
Feb 13 10:11:41 node2 Keepalived_vrrp[3486]: VRRP_Instance(VI_1) Entering BACKUP STATE
Feb 13 10:11:44 node2 Keepalived_vrrp[3486]: VRRP_Instance(VI_1) Transition to MASTER STATE
Feb 13 10:11:45 node2 Keepalived_vrrp[3486]: VRRP_Instance(VI_1) Entering MASTER STATE
Feb 13 10:11:47 node2 Keepalived_vrrp[3486]: VRRP_Instance(VI_1) Received advert with higher priority 150, ours 100
...

I had to restart keepalived on node1 to stop the ping pong game between the nodes.