What am I doing wrong?

So I like to consider myself an alocasia expert but this has me stumped. They’ve all been in pon for quite some time now so I know it’s not shock. In my experience, this looks like a fungal/bacterial issue.? But I’m not sure how it happened considering that I’m careful not to overfill the reservoirs, I don’t mist, I have them in ambient humidity, and they have good airflow… has anyone else run into this issue or have any theories? My next course of action is going to be to treat them with a disease control concentrate since that’s what I would do if they were in soil. Hopefully that helps.