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

Glad you fixed it

The logs show the following

Feb 24, 2019 15:57:14.245 [0x146379bff700] ERROR - Failed to calculate available disk space for path '"/transcode/Transcode/Sessions"': 1 (Operation not permitted)

and

Feb 24, 2019 15:57:14.296 [0x14637f3ca700] ERROR - [Transcoder] Could not write header for output file #0 (incorrect codec parameters ?): Permission denied

The issue appears to be with /transcode/Transcode/Sessions

Similar issue was reported here Conversion failed. The transcoder crashed or failed to start up. - #8 by sa2000