Can't access vault

I suggest contacting your M-Files reseller or whoever managed the cloud migration for you. Some additional configuration is likely required to enable federated authentication with Microsoft Entra ID.

Thank you so much for the response, but I forgot to also point out that the issue is peculiar to just two staff.

Could it still be be a federated authentication issue?

If everyone is using the same address to connect to the vault and are using the same authentication type (Windows) then the issue may be caused by something else. But if those users have login accounts which are configured to use M-Files authentication, for instance, then it could be normal behavior.