Ultra-air 120 dehumidifier

I have ultra air 120 that has been working great for about 2 years. We have it set up as entire house dehumidifier. About a week ago house starting feeling humid. I look at the unit seems to be working fine. Filter was change about 3 weeks ago so I did not think much of it. It start getting worst. I remove the filter and look at the coil and there is no condensation only upper and lower section completely ice up, frozen. I turn the unit off and let it tough through the next few days. I fire it back up with brand new heater and with in few min I can see upper and lower section icing up again. Nothing in the middle. I check if the fan inside is working, all good. I check air flow-all good, check for blockage in 10”hard pipe that is connected to the system all wide open. What can it be ? Is my coil restricted somewhere ? Does the this unit should defrost it self ? I did contact ultra air and left them a message since it’s still under warranty. Any input would be appreciated. Thank you

source https://hvac-talk.com/vbb/threads/2242624-Ultra-air-120-dehumidifier?goto=newpost