Long chats receive 504 gateway timeout in new copilot UI

A 504 means the web front end reached a gateway but the conversation request did not finish before the gateway's deadline. The blank page with starter prompts can occur when the Copilot shell loads but the history request fails, while Unable to load content is the handled version of a similar failure. None of those screens proves that the stored conversation was deleted.

Avoid repeatedly clearing cookies or deleting the conversation. Record its URL, title, approximate message count, account type, browser version, exact UTC failure time, and any request or correlation ID shown in the failed network response. Send that through Copilot feedback and Microsoft support. A browser network archive can contain authorization data, so attach it only to a private support case and do not post it in the forum.

Try the same conversation once from another Microsoft-supported browser or the Copilot app to separate a rendering problem from an account-side fetch timeout. If it opens intermittently, copy the important lore and decisions into a Word or OneNote document in manageable sections. For continued work, start a new chat with a concise, reviewed canon summary and links to those documents. Keep the original thread untouched so a server-side pagination or timeout fix can still recover access to it.