I noted this today on several leaves. I repotted the plant several weeks ago. It did fine until today. We had a nice cool spell for a couple of weeks then the weather got hot and humid again. It was in the 70’s and now upper 80’s.
The plant had good roots. It seems to have stabilized. I trimmed off all the dying leaves and hit it with physan a few times then returned it to it's sunny spot. I also treated it with insecticide, miticide and a systemic fungicide. Something worked