Phrag leaf rot: another

[JKeys]

So I have several phrags. I dealt with rot on one of them, but not another is showing symptoms.

Although it is actively growing (one mature, one baby growth) and has the healthiest root system if all of my phrags, it had popped out a tiny part of a new leaf on the mature growth. This didn't grow for a while but now is yellowing a little.

Anyone have advice for how to handle this situation?

Thanks so much, help is greatly appreciated.