Ghosting Latency Problem with External FX / Bus comp

Hi there,
I’m trying to do Hybrid analogue mixing, but the latency is not being compensated by the ‘Measure Delay’ ping button.
This is the set up:

Cubase Pro 12 (on Apple M1 silicon) into
Focusrite Clarett 8Pre thunderbolt interface to
Focusrite Clarett OctoPre via ADAT Toslink optical cable to
DB25 snake cable line output to
Warm Audio Bus-Comp2 to
Focusrite Clarett OctoPre via XLR into channel 3 & 4 (Send bus: Output 13 & 14. Return bus: ADAT 3 & 4) to
Focusrite Clarett 8Pre via ADAT Toslink optical cable to
Cubase Pro 12.

What seems to be happening is that, whilst it is routed from a plugin using External FX on the 2 bus (using Control Room), it sounds as if the audio is coming back in parallel to everything else (all other plugins) on the Master Buss , rather than within the plugin chain, if that makes sense. In other words, it kinda sounds like the audio being sent to the WA Bus-comp2 is not being effected by the signal chain).
To test this, I click mono on the Control Room & there seems to be a stereo layer of the sound still present, when it all should be mono.

It is impossible to mix with that amount of latency, which actually sounds like the signal is coming in earlier from the external compressor than the actual DAW.

WTF is going on here?

Any suggestions of how to resolve this issue?

How did you try to measure the delay?

How did you send the signal to the external FX?

I find hard to understand what you mean.

Can you simply use an External Effect as a channel insert, and test it for us?

For simplicity sake, I ‘always’ use the same channel number for input and output, in my external effect routing setup.

I use external effects all the time, I hope to be hrlpful

I have the same issue with my RME interface. Your ASIO driver is compensating for the delay of your interface analog converters. When you are using the ADAT to another converter, the delay is different (in my case it is faster, and what’s coming back from the external equipment is earlier than the reported analog delay from my RME device. What I have to do to get phase coherency is insert “Voxengo Sound Delay” plug-in with a 64 sample delay in the signal path to the external devices.

There is a measurement tool in the VST connection window available that does this for you.

Sure except that since the return from the external hardware is earlier than the ASIO delay, that number would be negative. Cubase cannot handle negative delay compensation.

Ha? What? No.