However, I'm not sure if it's due to different wear rates as it looks like it might be a stiff link.
Yes, the "as found" chain was not NOS, to say the least. I WD40ed it when first getting the bike ready for the road, working the links until it seemed OK to use. You can see one of the stiff link area just about to enter the lower jockey wheel...
But the "as found" chain worked just fine when the "as found" freewheel was still being used.
That said, I am pretty sure that the choice of freewheel is not the issue even though my brain knows that it was
the only thing that had changed. I hope to get some time today but it is looking less and less likely. Today, in addition to being "dump day" is also "yard sale day" and, since I have to go to the city to pick up supplies, I might as well keep winkin and blinkin peeled for...
who knows what