[Windows 10 Update KB4338819 issue] Conversion Failed. The transcoder exited due to an error

Which issue specifically?

This error in the log
ERROR - [Transcoder] [stream_segment,ssegment @ 026a4a80] Failed to open segment list 'http://127.0.0.1:32400/video/:/transcode/session/xxxxxxxxxxxxxx/seglist'
or the generic error Conversion Failed: The Transcoder exited due to an error ?

The generic error could be returned for many different underlying errors / issues. Have you posted logs anywhere of the problem?

If it is the 127.0.0.1 transcoder request erroring then have a look at my earlier post