Syncthing syncing from Receive only but not Send only

I have a few syncthing folders (including one 0.5TB and one 10TB) synced from a primary via send only to a secondary with receive only set.

I’m setting up a second secondary, and to speed up the initial sync have it connected to the same switch as the primary.

The other folders (including the 0.5TB) synced quickly, primarily from the send only local primary, but the 10TB seems to be only syncing from the (remote) secondary)

The new secondary reports that is is syncing from both, but no real traffic from the local primary:

from local primary: Download Rate [ 0 B/s (5.75 GiB) ] from remote secondary: Download Rate [ 500 KiB/s (74.1 GiB) ]

Is there anything I can do to diagnose?

Thanks

I don’t think the folder type should matter.

Does the send only device from its own perspective think its in sync?

You could also enable model debugging logs to see if there are requests coming in.