Why??

This Alocasia has been in perlite with water just below the roots the entire time I’ve had it. When I got it it had two leaves it since pushed out two more leaves and they have been growing great. Until now the only thing I can think of is the waterline is usually below the level of the roots and for a little bit it was above. When I inspected the roots there was no rotting, but I have no idea what else is causing this. Since this picture the last leaf has also died starting with these yellow spots. I see no bugs no eggs no webbing nothing. I normally treat with Captain Jack’s and systemic granules. It’s by window but doesn’t get direct light. Could this be because I haven’t been running the humidifier? I normally run about four or five hours a day. But haven’t prior to this. The only other change was the temperature increased in my house to about 85° when the air conditioning broke for three days normally it stays around 72. No watering, feeding or light has changed. I