Without knowing exactly what's in the soil or your watering habits my guess is one of two things or a combination of a few factors:
1. Overwatering - very common and can cause symptoms similar to what you see in the photo. I wouldn't want to flush the plant because it could make things worse from the added water. Need O2 in the rhizosphere.
2. Too much molasses, nutrients, aka food sources for microbes. This can cause the bacteria to bloom which produces heat and robs N. Basically the bacteria are more efficient at utilizing nutrients than the plant roots and will temporarily outcompete the plant for available nutrient sources. Think of a thermal compost pile but in your soil. Also that reproduction is an exothermic reaction, which adds heat (compost pile) and your roots aren't going to be happy with the increased soil temps.
Couple things to consider is all. Plant doesn't look too bad and should come back fine. I'd just wait it out.