Encoding. Formats 'MAGIX HEVC/AAC MP4', templates 'Internet HD 1080p 25 fps (Intel QSV)'.

Use this setting to  create an MP4 (HEVC/AAC) file for progressive internet downloads using Intel QSV encoder. Audio: 192 Kbps; 48.000 Hz; 16 Bit; Stereo; AAC
Video: 25 fps; 1920x1080 Progressive; NV12; 12 Mbps
Pixel Aspect Ratio: 1,000

=> BUT doing away with So4 Compoundreader also disables HEVC coding with QSV. I don't understand the connection.

So it means encoding with help of the Intel GPU by means of the Magix HEVEC codec.
That is not normal and I don't see that with VPro 17 latest build 387 on my laptop. So the reason has to be something else, f.i. GPU drivers not updated.
Look how it goes with me

Thank you j-v, you - inderectly - helped me a lot!

1. FYI: I work also with VEAS Pro17, build 387. And btw: QSV is NOT GPU but but a hardware implementation in the CPU (but that doesn't matter here).

2. You tried it, very good and helpful thank you, and indeed the rendering seems to be OK (on the preview screen), and the codingproces seems to run as expected. But the rendered outputfilefile is not OK. DivX player does not recognise the containerformat, Quick-Time gives an errorcode. Windows Media Player just plays 30 secs than freezes the video but the audio continues ...And importing in Vegas gives the same clue for that. Try it on a project > 2 minutes! Something wrong with timing in video vs audio (in my PC it starts going wrong after 31 sec).

3. The important clue is that you showed me that - if you set So4compound.. to FALSE - your Plug-In comes with mxhevcplug.dll. If I do the same, I end up with compoundplug.dll (while I found that mxhevcplug.dll is also available in my PC!). I don't understand why.

4. Anyhow that triggered me to experimentally try to set the Encodingmode in Mainconcept HEVC instead of Intel QSV in the Customize template section. Stupid, I never tried that before. Now everything works fine and encoding is much faster (3x)!

So, problem solved (without precisely understanding why).

=> Is there someone out there who understands it?

2. You tried it, very good and helpful thank you, and indeed the rendering seems to be OK (on the preview screen), and the codingproces seems to run as expected. But the rendered outputfilefile is not OK. DivX player does not recognise the containerformat, Quick-Time gives an errorcode. Windows Media Player just plays 30 secs than freezes the video but the audio continues ...And importing in Vegas gives the same clue for that. Try it on a project > 2 minutes! Something wrong with timing in video vs audio (in my PC it starts going wrong after 31 sec).

No i'm not gonna try for you 2 minutes of that slow encoder, my NVENC encodes it more tha 3 times faster.
The file I showed you I had rendered with and without the use of SO4 behaved both times the same and the MediaInfo of both files is this:

Both files played nice in Windows Films and TV, Windows MediaPlayer, VLC player and on the timeline of another Vegas instance, look for the last one

Yes, without trying QSV, but instead using your other HW/SW which I also believe is faster, your're fine but not me. That is essentially not what this forum is for.

Anyhow you triggerd me to find a workaround, I thank you for that!