SOLUTION: Conversion failed. The transcoder exited due to an error

Your failures are due to the faulty Windows 10 Update that Microsoft released on the 10th July and corrected in a subsequent Windows 10 Update on the 16th of July

The updates do get applied individually and a reboot may be needed between and the subsequent update would need another Check for Updates for it to be applies

Extract from your log

Aug 12, 2018 01:04:58.584 [3864] ERROR - [Transcoder] [stream_segment,ssegment @ 03ef7300] Failed to open segment list 'http://127.0.0.1:32400/video/:/transcode/session/gkr715a14zynrna8tmx3k9he/01bb0b78-4527-49be-9b10-594b055e1dd5/seglist'

Aug 12, 2018 01:04:58.611 [5464] ERROR - [Transcoder] av_interleaved_write_frame(): Unknown error

Aug 12, 2018 01:04:58.747 [12848] DEBUG - Jobs: 'C:\Program Files (x86)\Plex\Plex Media Server\PlexTranscoder.exe' exit code for process 11768 is 1 (failure)

The issue is covered by this forum thread. See the linked solution to the first post