Just sat down to do a simple trumpet line in Cubase and Halion SE. On a loop, do nothing at all, and the volume cuts really low. Metronome, samples, everything is fine. Volumes are all set correct.
Re-start Cubase. Do exactly the same thing again. All works fine. Then after a while, the volume cuts again.
Not a problem with my sound card.
Not a problem with any connections/speakers etc.
And really, this is the tip of the iceberg with this bug filled poop hole of a software package.
Is there a question hidden in your post somewhere?
Yes. Why the hell do I stick with Cubase when it constantly fails to deliver a stable, reliable platform?
That is a question only you can answer. The world is full of choices. Why continue to torture yourself if it is really that bad?
Alternatively, you could provide some kind of useful information. It might actually encourage someone else to help you with your problems
iangibson365, I hear you! I’m sick and tired too! Used Cubase 5 for 18 years. It was working pretty good but the software was starting to act funky so I thought it was time for a new PC and Cubase 10. So far it’s been one bummer after another. I want to create music not problem solve tech issues. Anyway good luck.
Addressing the audio cutout, the reduced volume, assuming you have created a Project, are you SEEING the volume drop off on the Stereo out bus? Or are you hearing the volume drop-off?
What you are describing is something I have never experienced in Cubase so…
Here’s an idea. When the cutout/drop-off in volume happens, record it and then export the recorded event and play it on an external player. Mix it to 16bit/44.1 and play it on an external device. Here at least you would put your soundcard device in the clear. Trying to help.
Once in a while I accidentally turn on automation on a track then sometime later reduce the volume on that particular track. Later on I’m thinking what the heck is going on when the volume keeps lowering… then I finally realize what happened. D’oh!!! 
100% this not a Cubase problem. i’m working 25 years on this platform.
The only thing that comes to my mind for your issue, is if for some reason that tumpet on Halion SE, maybe has a corrupted sample. Try to reinstall Halion SE
Steve, your edit to my post is understood 
. Sorry from me, as well.