I’ve had an issue with sidechaining using Cubase’s own built in compressor for a few versions now. What happens is that some of the instances are keying off a mix of the key signal (sent from a send) and the inserted tracks’ own audio.
For instance if I have a kick sent to a bass track I get a mixture of the kick and the bass triggering the bass’s compressor instead of just the kick. It only happens on some channels, others work fine.
Seems strange I have to use 3rd party compressors to get around this.