Known Copilot migration issue: missing chats, memory and custom instructions

After migrating to the new Microsoft Copilot experience, my personal Microsoft account lost a large part of its chat history, Saved Memories and Custom Instructions. The issue occurs on both Windows and the web.

Microsoft Support performed a remote repair without success. A later Copilot update also caused a pinned conversation to disappear.

During my latest support contact, the representative confirmed that this is a known issue affecting chat history, data, memory and custom instructions after migration. Microsoft engineers are reportedly working on a fix, but no estimated resolution date was provided.

Service version: 2.20261026.24.0

Subscription: Microsoft 365 Family

Country: Brazil

Support cases: 7109794789, 7110906183 and 7110907114.

Has anyone successfully recovered missing chats or had Saved Memories and Custom Instructions restored?