Note in my case this turned out to be human error. A chatgpt entry in the hosts file (for tcr9i.chat.openai.com) which had been added during a time when my network had DNS problems and not removed. Eventually the IP that tcr9i.chat.openai.com should point to changed, which stopped the web interface of ChatGPT working on the machine. By that time the memory of adding the entry to the hosts file had faded …