Could be the proxies messed up the FPS... NDF vs DF. or perhaps the sequence fps didn't match the source fps and you're seeing the mixed frame rate conform issue. Not sure there's an advantage to going back to source MXF on Canon stuff, if it's just rewrapped XDCAM anyway... IMO probably better off converting to DNxHD or ProRes to begin with. Not to mention what's the point when you're dealing with C300 footage. ;)
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