That looks like a water management issue caused by too much or too little moisture. Heres what I would do, I would very gently tip the plant out of the container and get a good look at the roots and soil. If the contents are overgrown with roots, it means the plant is not getting enough water. If the soil and roots are small and saturated or wet after watering, then the roots are suffering from excess moisture. You will lose leaves tipping it, but thats the only way to find out whats happening.
Just by looking, but not seeing, I think your plant needs a small increase in root space. If the root ball is large, up-pot only 2 inches in size. Using too big of a container to up-pot will hurt the plant, as it raises the water holding capacity too much. The only other thing that could be a problem is mealy bugs. Take a magnifier and look the plant over very closely.