I uploaded this issue to the Image Line team but they told me it was a bug that couldnt solve yet (this was two yrs ago), and it's still happening on fl studio 21

When you have more than one sidechain put in a mixer track. For example from kick to bass and from a piano to bass. The bass channel in mixer, for example using a fruity limiter to do sidechain, will have a number assigned following the sidechain route. This number frequently will split throught others channel asociatted to this bass. And it messed up the mix..

Does anybody have same issue?

 

Just send both piano and kick to a separate track and then sidechain that track to a bass track.

 

I also think putting each instrument on a separate channel will solve your problem.

 

There's also a way to lock a particular channel so that you can't modify what's already routed to it (i think)