Marty from Sunny Florida wrote:

The sky was clear, and when I got my pre-flight briefing, the temp was 26
and dew point 16. It was unseasonably cool and very dry for Florida. At
altitude, I knew the air had almost no moisture, but on the way up, we did
have a typical hazy layer.

Temp 26 and dewpoint 16 puts you well outside the icing region on this chart:

http://www.ez.org/carb_ice.htm

The temperature at altitude was probably well below 26, but even so you seem to
be pretty well outside the temperature / dewpoint danger zone.

Nevertheless, I agree with the consensus that carb ice is the best explanation.

I'm mystified that the chart doesn't confirm.

Dave