Expected behavior ..
The easiest fix is to update the encoded query on the Alerts tab in UI Builder.
Change the filter from something like:
source={{sysId}}
to:
source={{sysId}}^ORparent_alert.source={{sysId}}
This tells the list to also pull in any alert whose parent alert is linked to the incident, which covers your secondary/child alerts. You can do this directly in UI Builder by editing the data resource or list component configuration on the Incident record page in SOW.
If your hierarchy goes three or more levels deep, add another OR clause: ^ORparent_alert.parent_alert.source={{sysId}} — but for most setups, one extra level is enough.
