Great. I thought that too, but when I tried to recreate it again with a new session it somehow stopped working again?
Side-chaining
Maybe it’s just my .csd file. Are you using your own .csd file to test, or the one I sent just your earlier?
Yes, it is the same .csd file you sent me
When there is a plugin installed before, it modifies the path and stops working
Can you explain, I don’t quite follow?
I’m testing plugins with 4in - 4out, and if they are inserted before Sidecomp, they won’t let it work. But … It’s a Reaper problem, because with third-party pluins emulating the same situation, they produce the same effect.
Inserting them in this order is when it happens:
4in - 4out
4in - 2out, sidechain stops working
If the plugin that is inserted before Sidecomp, with 4in - 4out, channels 3 and 4 are bypassed, in the I / O selector, then it works again.
The 4in - 2out / 2in - 2out plugins do not give problems, when a plugin with sidechain is used after them.
Ok, so it’s a Reaper problem. I like to hear that! Not a Cabbage problem 
So I think we hit another side-chain milestone then? It appears to work fine in Reaper, Live and Logic? Now we need to double check Cubase…
Other well-known brand plugins react the same in Reaper with Audio Units.
For example:
First insert:
Voxengo voxformer
4in - 4out
Inserted after Voxformer:
FabFilter Pro C-2 (sidechain listening option, and internal-external switch
4in - 2out
Pro C-2, behaves in the same way as Compside (Voxformer occupies the 4 output channels and cancels the sidechain signal of the plugin that comes after). So there is no doubt that it is Reaper 
I’m going to review the tests again, but this is maturing 
You can see it here:
https://drive.google.com/file/d/1KFEd2O7IYld_wamQ3UvYwGUPCyJdytUn/view?usp=sharing
The latest tests with version 2.4.10 and Windows are as follows:
VST:
- Live (ok)
- Cubase (ok) without sidechain option
- Reaper (ok)
VST3:
- Live (as soon as the plugin is inserted there is no sound signal).
By assigning it a side chain it starts working correctly.
Returning to the (No Input) selection mutes or broadcasts
noises.
- Cubase (as soon as you insert it has a sound signal) it can be assigned
side chain and works properly.
When the side chain is turned off again, it goes silent or emits
noises, until you turn it on again.
- Reape r (ok)
This seems like something that could be an issue? I think we came across it before. I need to investigate whether there is a way fo determine if the side-chain has been deactivated.
I think it’s a good hint, the correct mono operation of VST3 in Cubase.
In stereo is when it gives the sidechain error