UniFi Site Manager: Multiple Devices Offline

Original query, unchanged.

let prev_offline_ids = Unifi_SiteManager_Devices_CL
    | where TimeGenerated between (ago(45m) .. ago(15m))
    | summarize arg_max(TimeGenerated, *) by Id
    | where Status == "offline"
    | distinct Id;
Unifi_SiteManager_Devices_CL
| where TimeGenerated > ago(15m)
| summarize arg_max(TimeGenerated, *) by Id
| where Status == "offline"
| extend IsNew = Id !in (prev_offline_ids)
| summarize
    OfflineDeviceCount = count(),
    NewlyOfflineCount = countif(IsNew),
    OfflineDevices = make_list(coalesce(Name, Id)),
    NewlyOfflineDevices = make_list_if(coalesce(Name, Id), IsNew),
    ProductLines = make_set(ProductLine)
| where OfflineDeviceCount >= 3
| where NewlyOfflineCount > 0
| extend
    TimeGenerated = now(),
    OfflineDeviceList = strcat_array(OfflineDevices, ", "),
    NewlyOfflineList = strcat_array(NewlyOfflineDevices, ", "),
    AffectedProductLines = strcat_array(ProductLines, ", ")
| extend Activity = strcat(NewlyOfflineCount, ' device(s) newly offline (', OfflineDeviceCount, ' total offline): ', NewlyOfflineList)
| project
    TimeGenerated,
    OfflineDeviceCount,
    NewlyOfflineCount,
    OfflineDeviceList,
    NewlyOfflineList,
    AffectedProductLines,
    Activity