I'm not sure it's a bug. THe KB updates KB4088785/KB4088776 are dated 13 March and not on 27 March.
I've two PC already working under W10 PRO latest updated version and my P3Dv4.2 works perfectly with FSUIPC 5.124.
For your information the latest W10 KB is just installed and it's the KB 4089848 dated 22th of March.
Improvements and fixes
This update includes quality improvements. No new operating system features are being introduced in this update. Key changes include:
Addresses issue with a GDI handle leak in the Windows Ribbon control.
Addresses issue where users can’t select OK after entering credentials in command line on Windows Server version 1709.
Addresses issues where Bluetooth devices fail to receive data after a restart.
Addresses issue where, during BitLocker decryption or encryption of a drive, files protected with the Encrypting File System (EFS) may become corrupted.
Addresses issue where the server may occasionally encounter an error during file transfer. The error is “Stop D1 in tcpip!TcpSegmentTcbSend”.
Addresses issue where an iSCSI RESET might trigger a cluster failover.
Addresses issue in MPIO where pass-through SCSI requests might lead to a stop error if the disk is pending removal.
Addresses issue where processing of group policies may fail, and policies may be removed as a result. This occurs if the length of the Windows Defender Firewall policy rule exceeds 260 characters.
Addresses issue caused by a new privilege in Windows Server 2016 and Windows 10 version 1709 named « Obtain an impersonation token for another user in the same session”. When applied using Group Policy to those computers, gpresult /h fails to generate reporting data for any setting configured by the Security Configuration Engine (SCE) extension. The error message is “Requested value ‘SeDelegateSessionUserImpersonatePrivilege’ was not found”. The Group Policy Management Console fails to show the privilege in the Settings tab for a GPO where the setting has been configured.
Addresses issue where errors may occur when accessing WebDAV files or folders on a SharePoint site if the file or folder name contains multibyte characters.
Addresses issue where the Remote Desktop License report gets corrupted when it exceeds the 4 KB size limit.
Addresses issue where an Azure point-to-site VPN connection that uses IKEv2 may fail when the user’s device contains a large number of trusted root certificates.
Addresses rendering issue in Microsoft Edge for PDF documents with backgrounds created using various third-party publishing tools.
Addresses issue where a media platform stops responding when changing cameras rapidly on a device.
Addresses issue where a media platform stops responding, which affects media playback in Microsoft Edge, Internet Explorer, and Microsoft PowerPoint.
Addresses issue with spatial audio when used in connection to Dolby Atmos for Headphones.
Addresses issue where a credential prompt that requires administrative privileges appears when a standard user account performs the first logon to a Windows 10 device that has been deployed using Windows Autopilot.
Addresses issue where tiles in the Start menu aren’t preserved when upgrading from Windows 10 version 1607 to Windows 10 version 1709.
Addresses issue with Spell Check and custom dictionaries.
Addresses issue with the press and hold feature when using a pen in Tablet mode.
Addresses issue with editing web password fields using a touch keyboard.
Addresses issue where some Bluetooth card readers don’t work after a restart.
If you installed earlier updates, only the new fixes in this package will be downloaded and installed on your device.
And I don't use Windows Defender
Hope this help