A good first step is to try to identify whether your issue is originating from the core LibVLC library or from the C# bindings code. This is not always straightforward to do.
To better understand what might be going on inside libvlc during playback in your application, verbose libvlc logs are helpful. To enable them, use this argument when creating your LibVLC object:
new LibVLC(enableDebugLogs: true);They should be printed to your Console, if you are building a Console project, or to the Visual Studio Output Window. Additionally, you may subscribe to the log messages in your code using libvlc.Log += ...
Some issues are platform specific, some are even device specific, or driver specific. Luckily LibVLCSharp runs on many platforms, so testing on various OSes is one way to try and pinpoint the original cause of the issue.
Enable debug logs in the official VLC apps and compare the logs with those from your application is yet another way to troubleshoot a problem.