Check Settings → Transcoder → Maximum simultaneous background video transcode.
If Unlimited, change to anything else and Save Changes.
There is a bug in 1.42.1.10060 that blocks background transcodes when the setting = Unlimited. There is separate bug where HEVC optimizations may have no video.
Both bugs are fixed in the current beta, 1.42.2.10102:
- (Downloads) Setting ‘Maximum simultaneous background video transcode’ to ‘Unlimited’ would prevent any download transcodes or optimizations from running (PM-3957)
- (Optimizations) HEVC Optimization could result in a file with no video (PM-3938)
