One of the environment that I had worked on as part of the Exchange Online migration involves the existence of Skype for Business.
For Exchange Online users that are provisioned for MFA, it has been reported that they encountered an error in Skype for Business client. "Exchange needs your credentials. Until then, you might see outdated info in Skype for Business".
Though this is not a hard error, this will result in stale Address Book Service (ABS), and intermittent Free/Busy presence issues.
To resolve this, add the registry key in the affected machines.
Then, apply the AllowAdalForNonLyncIndependentOfLync registry key setting: