To reproduce:

Render a timeline using the Audio Only preset, set to WAV (see that the Export Video box is unticked on the Video tab)
[Completed]
Now render the same timeline using a custom preset, set to MP4/AAC (see that the Export Video box is now ticked)
[Completed]Result:

The second render does not export video, but is audio only as with the first render.
To fix:
Untick and re-tick the Export Video checkbox to reset its state.
I have experienced this issue on Windows 10 from DR16.2 onwards, and it is still present in 17b5.