I am getting this same issue when I try to autosync footage shot at 59.97 with audio that has a TC of 23.98 (most of our project was shot at 23.98, but some clips were done on another camera at 59.97 so it would look more like video). I am wondering:
1) if you transcoded the footage within a project that is different than the footage was natively shot at, perhaps that is why you are now able to sync? Maybe this will effect your online. Before transcoding, it will warn you however.
2) If this isn’t your problem, have you figured it out? Because I do have the Framerate difference and it seems to work for me when I transcode the footage, but then I lose the proper framerate, and thus this solution will not work for me.
I’m in Avid MC 5.5