I just experienced this and it was a severe pain. I was trying to just drop a single line into a project and I had to turn off my control room off to hear signal during a take. I tried most everything from kicking out the bussing, to resetting my interface. Safe to say it was a fairly frustrating experience once I found it was control room in 5.1 causing the issue. I have used it in stereo before so it was one of those head scratchers for sure.