Left right speaker reversed

I thought it was an iPhone issue, but now it is the same in my studio monitors. Left and right speaker are reversed. When I pan hard right the sound comes from the left speaker. And yes, I have the setup correct, this happened all of a sudden. I have had this problem when I listen to my mixes from my iPhone so I thought that the iPhone randomly changed the left/right speaker for some reason. But now when it happens on my iMac in the studio it’s a big issue. What can I do to fix this problem?