Hello!
It sounds like you're experiencing an issue with Multi-Factor Authentication (MFA) not working correctly in two clients who are subscribers of Microsoft 365 under the NFP licensing program.
Firstly, it's important to note that the NFP licensing program for Microsoft 365 is specifically designed for nonprofit organizations, providing discounted pricing and access to certain features. While this program may have different constraints and configurations than other licensing programs, it should still be possible to use MFA effectively.
In terms of resources, Microsoft has a comprehensive guide on enabling and configuring MFA for Microsoft 365 users, which you may find helpful. Additionally, Microsoft offers free technical support for subscribers of Microsoft 365, so you may want to consider reaching out to them directly for assistance with this issue.
That being said, it's worth noting that MFA behavior can vary depending on the authentication method used. For example, users accessing Microsoft 365 from a trusted device or network location may not be prompted for MFA every time they log in. Additionally, some apps and services may not support MFA at all.
In your case, if you've already verified that MFA is enabled and mandatory for all users in both clients, it may be worth checking the specific MFA settings for each user to ensure they are correctly configured. This method can be done via the Microsoft 365 admin center or PowerShell.
I hope this information helps! Please let me know if you have any further questions or concerns.