The sunshade was binding about six inches from being fully open. I looked and found the RH rail had popped out of the clip.
I got some silicone spray and coated the rails on both sides using a Q-tip. (You can open the sunshade by slowly rolling the take-up roller in the middle by hand rather than pushing on the center handle.)
I made one application then closed and opened it again and made a second application (again using the Q-tip) and now everything seems to work as designed.
The binding would cause the rail to pop out of the clip - which BTW HAS to be "U" shaped to allow the fabric to pass thru (someone earlier suggested it should be closed.)
I'll keep tabs on this fix and see if it holds up.