Problem with Server transcoding

[JonW]

I routinely use BubbleUPnP  to cast videos to Chromecast.

I run the BubbleUPnP app on my Android phone and BubbleUPnP Server on a PC on my home network.

The app is configured to "Prefer remote BubbleUPnP Server transcoding".

"Force video transcode" is usually 'off' — but it doesn't fix the problem if I set it 'on'.

Most of the time everything works just fine (thanks!).

The problem is that with some video files I get audio, but no video.

The most recent file for which video didn't work was an MKV file containing

Video: HEVC

Audio: AAC LC

I suspect it has also affected other contained video formats, although I haven't kept a note.

But if I change "Prefer remote transcoding" to "Prefer local" in the app, it works.  

It seems odd that an Android phone can do what a reasonably powerful PC can't.  So, I'm guessing that something is wrong with the config of my BubbleUPnP server, but I just can't work out what the issue is.

This is the Status of my BubbleUPnP server:

  Version:  0.9-update40

  Audio Transcoding supported:   yes

  Video Transcoding supported:   yes

  Image Transcoding supported:  yes

I've had a look at "Chromecast transcoding" in the Help but I'm not clear what other Server settings I should be looking at, or what they should be set to.

Thanks in advance for any and all help.