I have had this problem a number of times, especially when you put a new drive in the mix. You will have to trash your settings. Use the following link to get the freeware program and it will guide you through trashing your settings. https://www.macupdate.com/info.php/id/14729 Once you use this program, you will have to redo your settings. Hope it helps,
Click on the viewer screen and hit the option and Z, that will turn on the timecode overlay, which will show you the timecode of your audio and video sources. You can then do the same to the canvas side. Hope it helps.