In my case, it only happens on this one project. All other projects are fine. This would tell me it's not in my monitoring chain. This happened one or two other times (In many years) and I ended up copying each track file to a new template and all was fine. (A very time consuming fix BTW) Something had to have happened in that particular Sonar project. Right?
Also, yes, my meters in Sonar show correct panning but, what Sonar is outputting is not correct.