Alert check for Device rebooted won't work in r13020

Hello,
We updated our Observium instances last week to revision 13020 and after a couple of days found out that the Alert checkers for "Device rebooted" didn't work.
What we have found so far is that the state in the table "Alert_id" is "{"metrics":{"device_rebooted":null}}" while the expected value is either "{"metrics":{"device_rebooted":0}}" or "{"metrics":{"device_rebooted":1}}"

When manually discovering a random device, this is what the discover.php returns:
[root@mum-obs-2.vm: /opt/observium]# ./poller.php -d -h mmrda-rsb-h-s5735-acc | grep rebooted
    [last_rebooted] => 1695423984
    [last_rebooted] => 1695423984
    [rebooted] => 0

But as a record in the Alert_id table we have: :{\"device_rebooted\":null}}.

Downgrading to revision 12912 which was our previous version fixed the issue.