Sometimes manual sessions can fail, such as when the session ends immediately when the device interface just shows up for a few seconds. The error message shown underneath the device screen interface could be “HTTP response at 400 or 500 level”, or “Session not found”. If the behavior recurs, we need to make sure the error message in the Chrome console log contain “ERR_NETWORK_CHANGED” (like in the screenshot below).
In this case, we need to make sure that Chrome browser is trusted or allowed by the antivirus software/app on the machine being used to launch the manual session. Refer to this article: https://support.google.com/chrome/thread/5053885/err-network-changed?hl=en