Same issue. Unfortunately the only “temporary fix” for me was to restart the PC. When restarting the UnrealTraceServer I got the same issue, so it was useless.
EDIT: As I mentioned on another post (Unreal Insights Does not Connect to Server - #4 by Scienziatogm), maybe I’ve found a fix: disable all the network adapters except the main ethernet/wifi adapter, terminate the UnrealTraceServer.exe process, close the editor and open it again. These steps worked for me without restarting the PC.