Microsoft recently released a bunch of cumulative updates for Windows 10 version 1809 to fix several issues. Unfortunately, it looks like one of those updates managed to break the media player in Windows 10.
Microsoft has now acknowledged that the seek bar in Media Player is broken after downloading the new patches. The issue was discovered after installing KB4467708 (OS Build 17763.134) on Windows 10, version 1809 (October 2018 Update).
After installing this update, users may not be able to use the Seek Bar in Windows Media Player when playing specific files. Microsoft is working on a resolution and will provide an update in an upcoming release.
Not only that, but users have also reported that some first-party system apps like Notepad are having issues. Microsoft has confirmed that they are working on a solution and users can expect cumulative updates to fix those specific issues soon.