One of the issues with the October 2018 Windows 10 Update (1809) was the seek bar may not work in Windows Mixed Player. Microsoft have now fixed this with a cumulative update for Windows 10. KB4471332 takes the OS to version 17763.194.
This update includes quality improvements. No new operating system features are being introduced in this update. Key changes include:
Addresses an issue that may prevent the use of the Seek Bar in Windows Media Player when playing specific files. This issue does not affect normal playback.
Security updates to Windows Authentication, Microsoft Scripting Engine, Internet Explorer, Windows App Platform and Frameworks, Microsoft Graphics Component, Windows Storage and Filesystems, Windows Wireless Networking, Windows Kernel, Microsoft Edge, and Microsoft Scripting Engine.