I’ve had exactly the same problem with my 2009 Reba WC. I took the damper out, gave it a good clean up and soaked it in suspension oil.
The fault wasn’t the cable like a initially thought.
It seems to be a temperature related malfunction. Above ambient temperatures in the mid 20’s, the damper starts to stick. I tested it by putting the damper in the freezer for a bit and it was totally friction free.
I suspect it is the result of the incorrect specification of the plastic used in the damper, and/or the tolerence of the hole tht the steel shaft runs in down the middle. The modulus of thermal expansion of the plastic would appear too high for the design.
Still, that doesn’t solve the problem. On this analysis I’d say it might help if the plastic was drilled out slightly allowing the shaft to run more freely, but because it is a factory assembled unit that can’t be dis-assembled, that’s not really viable. I think replacing the top cap with a manual knob would be the easiest solution to over come the excessive friction; shame though as its not actually the cable and lever at fault.