Mold smell from heat pump/ac

Hello All,

Our problem [ hopefully someone can help] involves a smell coming from our heat pump/air conditioner. First we thought it was a mold smell...we installed UV lights, had ducts fogged..and finally put in a whole house dehumidifier.[sized for the house sq ft]
Smell is very caustic...not all people smell it...gets to my throat and eyes tear.
The dehumidifier seems to help until it gets very humid outside. Humidify gauge shows 55% of air coming out of vents and the gauge set in individual rooms can show 60%, even though the humidifier is set to full. When rooms % shows 57% I start to get the smell.
There is no visible mold in the ducts. I have heard of dirty sock syndrome. Could this smell be dirty sock syndrome? I've read that this smell is not irritating.
Is the smell from dirty sock influenced by the humidity? We did not have ducts fogged for this.

Does anyone have any idea what is going on here ...AND what can be done to get rid of the smell?

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