Multiple Copilot notebooks disappeared immediately after sync

Today, after a Copilot synchronisation event, multiple notebooks disappeared from my account.

I observed the notebooks briefly appear on a second device (MacBook Air) and then disappear during synchronisation.

One missing notebook is called VIT. Several other notebooks also disappeared at the same time. Chats associated with those notebooks are no longer visible in chat history.

Other notebooks remain visible. One remaining notebook ("8 STEM") displays the message:

"Limit reached: Copilot can chat about the 20 oldest items in your notebook."

The timing strongly suggests a synchronisation or migration issue rather than accidental deletion.

This content represents a substantial amount of teaching-related work and planning material. Can Microsoft confirm whether the missing notebook and chat data still exists on the backend and whether there is a way to force a resynchronisation?

Additional observations:

The notebooks existed prior to the sync.

Notebooks were briefly visible, then disappeared.

The issue occurs across multiple devices.

Associated chats are also missing.