An invalid response was received from the upstream server for Keycloak

I try to connect Keycloak and sometime it return

{
  "message": "An invalid response was received from the upstream server"
}

cannot access to my Keycloak but sometime works fine. The temporary way to fix it is “close browser and re-open again” this error message will gone and will come back again like a loop error.

Anyone can recommend me how to solve this ?