I dug into the data more, finding all the activities that completed the other nodes and then manually checking nearby nodes for those. I found one activity that would return those 6 nodes.
The issue is that an optimization I added to the processing that occurs after a city sync isn’t working as expected. There are some cases where matching activities are excluded from the query.
This also explains what’s going on in Vancouver progress now inaccurate … which is good and bad 
I’m pausing city syncs until I get this sorted out.