Multicam sync problem

I am having a problem syncing clips with Multicam. The source clips are 2 video-audio clips from 2 different cameras and 2 other audio clips from a Zoom recorder which was recording simultaneously with the cameras. The 2 camera clips and 1 of the Zoom clips sync up perfectly. But the second Zoom clip (which is only a few dBs quieter) keeps getting placed at the end of the new Multicam Clip, instead being synced with it. I have attached a photo. You can see the 2 Zoom tracks placed sequentially instead of in sync with each other. I have no idea what is causing this. Does anyone know?