Threads hanging after first message

This is occurring on GPT-5 and DeepSeek R1, so I assume it’s happening with every model: I ask the initial question and the model returns a response. The thread appears in the left pane but it just says “New Thread” and has a loading spinner that never goes away. When I type a second message into the chat prompt and hit return it does not send or do anything else, so I cannot continue the thread from there.