Hi MajinChaos,
Thank you for posting in the Microsoft Community Forums.
Roll back system updates:
If possible, consider rolling back affected PCs to a pre-update system version to restore Guest logon functionality. This can be done via the “Restore” option in the Windows Update settings, but note that this may require administrator privileges.
Check and update Group Policy:
On the domain controller, check the Group Policy settings related to the SharedPC feature and Guest logon. Ensure that these settings are not blocking Guest account logins and are consistent with the school's IT policies and security requirements.
Modify the local security policy:
On the affected PCs, check and modify the security policy related to Guest logins through the local security policy editor (secpol.msc). For example, ensure that “Network Access: Shared and Secure Mode for Local Users” is set to allow Guest access.
4724(S, F) An attempt was made to reset an account's password. - Windows 10 | Microsoft Learn
Best regards
Neuvi