I heard @Omri_Cohen mention this in a video recently and have just experienced it using MindMeld. There are certain unknown conditions where having sends/returns set up with a mixer can cause Rack to output silence but an apparent constant signal through the aux channels. It is very similar to this bug which is making me think that it is either the same bug somewhere in a plugin or it is something in Rack itself.
I’m just wondering if anyone has managed to narrow down the problem. I always seem to get it either loading a patch (although I haven’t experienced this for a while) or in the middle of noodling and something causes a high output, such as a filter resonance too high. I think it has been suggested that it’s a bug in Plateau, which would certainly fit for me, but I think I’ve seen people experiencing the same thing with NYSTHI’s reverbs.