There is an FString error while using the IHttpRequest URL. Please help.

I created a process to receive and process data from the server via GET using IHttpRequest, and the request is made about 10 times per second.
Within 1 to 2 minutes after execution, a strange value appears at the beginning of the FString type URL variable.
I copied the string in various other forms or created a new one and used it, but the same problem occurs.
If anyone has experienced the same problem as me or knows a solution, please help.
thank you