Not seeing other plants, so after that time frame I doubt disease.
Never used a self-watering pot, but to me to looks like too little moisture.
If the soil is dry to 2" and you water a given amount, the soil/roots/plant will probably get a very small bit, the rest will drain off, and the root core and surrounding soil will still be dry.
When *some* plants are thirsty they want to be quenched thoroughly enough that they can access the moisture for the duration they need, but not so much it's still soggy after they get it.
Drainage and occasional drenchings have done well for me at least.
