Trouble replacing new models through the API

That’s look like load model failed. When you initiate a POST request, how about the response? BTW, depend on the api doc. You can directly try this one, (if the model in your local dir):

curl -X PUT  \
  'http://localhost:5005/model' \
 \
  -d '{
  "model_file": "/models/20190512.tar.gz",
}'