I upgraded to 2020 a couple of days ago and had a similar issue using Sonar (well, BandLab as it's called these days). When I dragged a bass track over to the Dropbox and then to my DAW, the adjacent guitar track would be mixed in there with the bass as a single track. I double-checked to confirm "Always allow Drag and Drop" and "Drag as separate tracks" were checked. I also checked the track to see if they could be separated. They could not. However, this problem solved itself after updating to build 706.