Bert Coules wrote

I'm pretty certain that it's not a lack-of-lubricant issue. The dead
stop, when it happens, is an abrupt halt, not an increasing-resistance
petering out of movement.

I'm not sure exactly how these blinds function but there's a curious
runner, unlike any of the others and not attached to a slat, which appears
to be playing a part in the problem.

Yeah, very likely. How does that compare with the other one that still works
fine ?

I just tried to upload a picture to my website but discovered that my FTP
program doesn't seem to be working any more.

Very easy to use dropbox on your phone instead.