Detect instances of multiple server errors occurring within a brief period of time (ASIM Web Session)

Original query, unchanged.

// HTTP response status codes indicate whether a specific HTTP request has been successfully completed.
// Please refer this for more details: https://developer.mozilla.org/en-US/docs/Web/HTTP/Status
let threshold = 100; // You can update threshold value as per your environment
_Im_WebSession(starttime=ago(1h))
| where toint(EventResultDetails) between (500 .. 599)
| summarize
    TotalErrorCount = count(),
    URLs=make_set(Url, 100),
    EventStartTime = min(TimeGenerated),
    EventEndTime = max(TimeGenerated),
    EventResultDetailsSet=make_set(EventResultDetails,10)
    by SrcIpAddr, bin(TimeGenerated, 5m), SrcUsername, SrcHostname
| where TotalErrorCount > threshold
| extend
    Name = iif(SrcUsername contains "@", tostring(split(SrcUsername, '@', 0)[0]), SrcUsername),
    UPNSuffix = iif(SrcUsername contains "@", tostring(split(SrcUsername, '@', 1)[0]), ""), Threshold=threshold