Question: There is a spike in Front end server and reason for that is ScriptError.asmx is getting called continuously.
Answer: ScriptError.asmx is called when CRM is not able handle the internal error. When you do the fiddler and see that /AppWebServices/ScriptError.asmx url is getting called multiple times.
The potential fix for this can be it is trying to send the Watson error to Microsoft. To avoid that change below privacy setting.
Go to Settings –> Administration –> Privacy Settings
Under error reporting, change the setting “Never send an error report to Microsoft”
This will fix the issue.