Not only you. In my case I had 2 identical monitors both attached to USB-C-to-DisplayPort cables on a 2019 MacBook Pro, and the left and right monitors would sw

Not only you. In my case I had 2 identical monitors both attached to USB-C-to-DisplayPort cables on a 2019 MacBook Pro, and the left and right monitors would swap daily. Fortunately my monitors also had USB-C input; switching one monitor to USB-C-to-USB-C and leaving the other USB-C-to-DisplayPort seems to make the screen ordering mostly more stable. However the OS still moves all windows to the left monitor weekly, so it's not fully working.