Had the same problem with Wisteria. It's an aquatic weed and as such, a nitrate hog. It basically grew so large that it starved to death (well of course I didn't add ferts but that was the intention of the tank). This was in a heavily planted and heavily stocked tank.
When it did go through this phase, it looked similar to yours and had mats of roots growing at all levels of the stem(s).
I do not recommend this plant for low-tech tanks that do not have a regular fert regime. It looks great growing but then it outgrows such a tank's nitrate levels.