Certain Conversations in Copilot Work Account Disappeared from My Account History

There are dozens of conversations missing from my Microsoft Copilot history. My entire history isn't gone, but there are specific months and weeks where I was brainstorming and editing documents for work that are entirely gone. For example, I was working on a number of projects on December 26/27, 2025 that are gone when I logged in today January 10, 2026. I did not delete them. Can someone help me understand why some conversations are gone and others retained, within the same account? And if there is a way to get back the lost conversations? This has never happened before and now there's a lot of lost work I have to re-create.