Your plant has an internal infection.

If you look at the very top....you will see a black spot that sits where a fan leaf has been plucked, pulled, cut, eaten or whatever. The black spot is likely the point of entry into the plant.

As well you have a major bug / predator problem.

The infection is systemic and probably there is nothing you can do, topically, to alter its course.

This IS NOT a cold weather issue or a pH or nutrient lack problem. Its an internal sickness / disease brought about by nature and your plant was exposed by vermin or something else in the open the wound.

It could even be caused by toxic water splashing off the cracked paint or whatever it is on the backside of the structure.

Either way, it will start with the youngest most infantile foilage and then work its way down thru the healthier, more vigorous green.

PROGNOSIS: Probable eventual death.

Sorry.