Determining which files won't sync

I've had this for a couple of weeks now on one Mac. I'm pretty sure it's the same five files all the time, although the size does vary slightly from day to day.

All other files are syncing in both directions without a problem. I have several Macs so I can confirm this. I don't use optimisation on this Mac (should it make any difference)

How do I determine which files these are? If I can locate them, I can look at them to decide what action to take.