development server has disconnect

[WinterLLL]

I'm currently working on a django project with a tutorial from youtube. I'm trying to build an website like twitter with using the react-app too. In the tutorial you can see the tweetslist and a field for writing a tweet on the react website, but in my case nothing is there. I start looking for mistskes but I can't find some and when I run the server no issues pop up. On the website I get the alert:
The development server has disconnected.
Refresh the page if necessary.
[HMR] Waiting for update signal from WDS...
I reloaded the development server many times and refreshed the page too. Has someone worked with this and could help me please.